pcb electronics testing technology

In the field of electronic product manufacturing, the testing technology involved includes but is not limited to the following items: Chip component incoming inspection technology, incoming inspection size measurement technology, incoming inspection weldability testing technology, metal parts and non-metallic parts coating measurement technology, composition testing technology, temperature resistance testing technology, material expansion coefficient testing technology, polymer material Tg point measurement technology, hardness measurement technology, corrosion resistance measurement technology, chemical corrosion measurement technology, viscosity measurement technology, bond strength measurement technology, Solder joint strength measurement technology, electromagnetic shielding technology, heat conductivity measurement technology, optical detection technology, current and voltage measurement technology, steel plate incoming inspection process, solderpaste incoming inspection process, PCB incoming inspection process, label quality inspection technology, equipment motion accuracy testing technology, two-dimensional and three-dimensional detection technology, SPI process technology, AOI process, Reflow temperature measurement technology, Reflow temperature monitoring system, Reflow wind speed measurement technology, Reflow Oxygen Concentration Measurement Technology, Orbital Deformation Measurement Technology, Wave Soldering Temperature Measurement Technology, Wave Soldering FluxSpraying Uniformity Measurement Technology, Tin Wave Height Measurement Technology, Tin Bath Composition Measurement Technology, Solder Paste, Solder Wire, Flux Corrosivity Detection Technology, ICT Process, FCT Process, High Temperature and High Humidity Test, High Temperature Storage Test, Surface Insulation Resistance Test, Electrochemical Migration Test, Tin Whisker Test, Temperature Shock Test, Temperature Cycle Test, High Temperature Aging Test, Drum Test, Drop Test, Mechanical Shock Test, Vibration Test, Slice Analysis, Red Ink Test, Ion Residual Concentration Test, Metallographic Testing, Non-metallic Material Composition Test & Crystallization Test, Adhesive Curing Rate Test, Hardness Test, Transmittance Test, Refractive Index Test, Metallurgical Microscope Application Technology, Electron Scanning Microscope Application Technology, Focused Ion Beam (FIB) Testing Technology, Auger Microscopy Technology (AES), Transmission Electron Microscopy Technology, Infrared Spectroscopy Analysis Technology, Atomic Probe Technology, Thermal Simulation Technology, Structural simulation technology, integrated circuit characteristic measurement technology, etc. Here, the author only makes a basic elaboration on the commonly used detection technologies of PCBA, focusing on the application timing, application fields, benefits to daily production, and blind spots in detection management. In order to facilitate the application of colleagues and the reference of the division of management responsibilities, the testing is temporarily divided into four main parts: incoming inspection and testing, PCBA production management testing, assembly testing, and laboratory testing.

1. Incoming inspection and testing technology There are many incoming inspection and testing technologies, and the following types are higher in daily use: solder paste incoming inspection technology, steel plate incoming inspection technology, PCB incoming inspection technology, Chip incoming inspection technology, IC component incoming inspection technology, component solderability testing technology, connector temperature resistance inspection technology, structural parts incoming inspection technology, wire harness incoming inspection technology, packaging material incoming inspection technology, chemical incoming inspection technology, Tin bar and tin wire feeding inspection technology, etc.

(1) Solder paste feed inspection technology The commonly used items for solder paste feed inspection include viscosity test, flux content test, copper mirror test, diffusion test, collapse test, solder bead test, tin powder particle size and shape test, tin powder oxygen content test, tin powder alloy composition test, etc.

1.Solder Paste Viscosity Testing Solder paste viscosity testing is the most widely used incoming inspection program to measure the dynamic viscosity of the physical properties of solder paste, usually with the help of a viscosity tester. In solder paste viscosity testing, a common problem is that the test results are unstable. For example, after the same batch of solder paste is warmed and stirred, the viscosity value measured by two bottles of solder paste may be quite different, one bottle has a viscosity value of 240Pa.s, and the other bottle has a viscosity value of 170Pa.s, and the results obtained by two tests of the same bottle of solder paste are difficult to be the same. This phenomenon of unstable test values has brought trouble to the daily incoming inspection work of colleagues. When the viscosity values obtained by the test are outside the specification range, both the tester and the supplier will be skeptical of the test results. It is important to note that solder paste viscosity is a dynamic value, which is susceptible to external factors, such as the number of manual stirring, stirring speed, how long after stirring to measure, etc. In principle, the viscosity of solder paste is tested according to IPC-TM-650 2.4.44 or according to JIS Z 3284, and the viscosity value measured under the conditions of fixed speed, fixed test time, fixed test environment temperature and fixed test pre-treatment is within a certain range, and the deviation is not too large. The reason for the large deviation of the test value is due to the change of certain factors. In addition, the inspectors perform operations in accordance with international standards, and on the premise of confirming that the implementation requirements are not exceeded, if the measured solder paste viscosity exceeds the standard, the viscosity of the solder paste can be judged to be unqualified. For example, if the viscosity specification of solder paste is 150 pa.s - 250 Pa.s, the viscosity value of 3 minutes and 5 minutes is read, and if it exceeds the specification, it will be judged to be unqualified. In order to avoid disputes over the test results, the solder paste specification needs to specify the test protocol and the conditions under which the test values can be read.

2.Flux content test The change of flux content in solder paste will directly affect the active ingredient (tin powder) of solder paste, which has a direct reflection of the amount of tin in the solder joint. The specific gravity of the solder paste flux is lighter, and the flux content changes by 0.5%, which means that the flux has a large increase or decrease in volume. Assuming that the flux content in the solder paste is 10% and the flux accounts for 50% of the solder paste volume, that is, 1% flux accounts for 5% of the total volume of the solder paste, and the difference in flux quality of 0.5% will result in a change in the volume of the solder paste by about 2.5%. To put it simply, after a certain amount of solder paste is melted, the flux residue is cleaned off with a solvent, the obtained metal quality is weighed, and compared with the original solder paste quality, the solder paste flux content and the solder paste metal content can be obtained. You can also weigh a certain amount of solder paste, directly clean it with solvent to obtain tin powder particles, and dry it to obtain the metal content of solder paste and flux content. Solder paste flux content testing is generally not managed as a mandatory incoming inspection, and is commonly used in the confirmation analysis process when there is generally little tin in solder joints and the flux residue is seriously exceeded.

3.Copper mirror test This test is often used to measure the corrosivity of solder paste flux during solder paste evaluation and identification, and is not a mandatory management content for solder paste incoming inspection. When solder joint corrosion and electrochemical migration occur, some companies will measure the copper mirror test of solder paste to determine whether the corrosiveness of solder paste flux exceeds the standard. For specific operation procedures and judgment criteria, please refer to JIS Z 3197 or J - STD - 004.

4.Diffusion test Solder paste diffusion test is one of the key indicators of soldering characteristics of solder paste, which is a comprehensive embodiment of solder paste solder powder composition, solder paste oxygen content, flux activity and other factors, which has a direct impact on the solder climbing height, solder joint wetting angle and solder spreading rate in the actual soldering process. The solder diffusion test is not managed as a mandatory control item for daily incoming inspection, and the specific operation method and interpretation standard refer to JIS Z 3197. In the industry, when there are abnormalities such as dewetting and poor solder climbing, the solder diffusivity test is used to determine whether the abnormal solder joints of the product are due to abnormal PCB solderability, poor component solderability, or abnormal solder paste characteristics.

5.Collapse test The collapse test of solder paste is divided into two types: cold collapse and hot collapse. Cold collapse is used to evaluate the ability of solder paste to maintain its shape at room temperature after printing; Thermal collapse is to evaluate the characteristics of the deformation of solder paste after printing and entering the reflow oven after heating. The cold collapse and thermal collapse test is an effective test item to evaluate whether the solder paste is suitable for the soldering of close-pitch components, that is, to evaluate its ability to prevent short-circuit of solder joints in close-pitch components, and it is a mandatory test item for the evaluation and identification of solder paste. Although it is not required to be included in the mandatory control content of daily incoming material inspection, it is still the main control content of solder paste characteristics. Generally, when a company encounters a serious short circuit in a close-pitch device during the production process, it will perform a collapse test to determine whether the characteristics of the solder paste have deviated, resulting in a short circuit. Please refer to JIS Z 3284 and J - STD - 005A for collapse test standards and operations.

6.Solder Bead Test The solder bead test is the most widely performed and effective test item in addition to viscosity test. The standard and operation of the solder bead test can be found in Section 11 of Annex JIS Z 3284. The solder bead test is a comprehensive embodiment of factors such as the oxygen content of solder powder, the shape of solder powder, the quality control of solder paste stirring process, the characteristics of solder paste flux, and the storage and transportation conditions of solder paste. Because of its simple operation, no need for special equipment and easy implementation, it has become a widely used and effective monitoring and analysis tool in the industry. Unlike solder paste viscosity testing, which requires a dedicated viscosity tester, solder bead testing can be performed without investing in any fixed assets. The standard solder bead test is to print a round solder paste with a diameter of 6.5mm on a clean ceramic sheet, use a constant temperature tin bath to heat the ceramic sheet to melt the paste solder to form a large size solder ball, and judge whether the quality of the solder paste is qualified by observing the residual size and quantity of small solder balls around the large size solder ball. The simple method is to print the solder paste in the large area of the PCB, heat the PCB through Reflow or use a heating platform (teppanyaki) or a small solder pot to melt the solder paste into a ball, and observe the number and size of the small solder beads around to determine whether the quality of the solder paste is qualified. Some companies purchase ceramic chips and small-size glass fiber boards to complete the tin bead test. The tin bead test is an effective low-cost and high-value testing project in the industry because of its simple operation, no need for fixed assets, and high comprehensiveness of inspection results.

7.Solder Powder Particle Size and Shape Test Solder paste and solder powder particle size and shape are common inspection items to evaluate the quality of solder paste, which is simple to operate and the results are intuitive and effective. The particle size of the tin powder determines the minimum size of the opening of the steel plate and the thickness of the steel plate, and the shape of the tin powder affects the viscosity of the solder paste and the printing quality of the solder paste. Solder paste manufacturers use image projectors to automatically measure the size and shape of solder powder, and PCBA factories can use metallurgical microscopes or high-magnification 3D microscopes to measure directly. Although the industry does not include the particle size of solder paste and solder powder in the daily management of incoming inspection, many factories still occasionally measure the particle size and shape of the solder paste they use to monitor whether the quality of the solder paste has changed. Tin powder particle size and shape test is commonly used in the analysis of the anomaly of less tin printing in the production line, generally the solder paste plugged hole on the steel plate is collected on the steel plate cleaning paper, or the solder paste on the pad printed with less tin on the PCB can be collected, and part of the solder paste can be collected directly from the steel plate, and the solder powder particles can also be collected from the used solder paste bottle using IPA solvent, and the collected solder paste is cleaned with alcohol or IPA, and after the flux is removed, the size and shape of the tin powder particles are measured by a metallographic microscope and a 3D microscope.

8.Tin powder oxygen content test Tin powder oxygen content is one of the key indicators of tin powder quality, especially for Tin powder above Type 5, such as Type 6, Type 7 or even No. 8 powder, No. 9 powder, etc. The oxygen content of tin powder directly affects the main indicators such as solder ball residue, solder joint brightness, and solder wetting effect during soldering. The oxygen content test of tin powder requires professional equipment and personnel, and generally does not require the implementation of incoming inspection, and the industry's alternative simple test scheme is the solder bead test.

9.Tin powder alloy composition test Tin powder alloy composition test is generally not used as a daily incoming inspection control item, but is mostly used in the evaluation and identification of solder paste, and is also used to check whether the melting point of solder drifts when soldering is abnormal.

(2) Steel plate feeding inspection technology The steel plate feeding inspection includes the number of openings (less opening, more opening), opening position accuracy, opening size accuracy, hole wall roughness, steel plate tension, steel plate thickness, etc. There are two commonly used schemes in the industry: steel plate feeding inspection platform and steel plate inspection machine. The steel plate inspection machine integrates tension test, hole size test, steel plate thickness test, position accuracy test and other items. The standard file used by the steel plate inspection machine is the steel plate opening file, if there are fewer holes in the opening file, the steel plate inspection machine can not find more holes and fewer holes in advance. The steel plate inspection machine needs to have the ability of PCB Gerber file recognition, and compare the original PCB design file with the steel plate manufacturer's perforation data, so as to effectively avoid the phenomenon of missing perforated steel plate online production. Another problem is that the detection ability of the steel plate opening position accuracy depends on the accuracy of the motion system of the steel plate inspection machine, if the accuracy of the motion system of the steel plate inspection machine is insufficient, the appearance of the steel plate opening position deviation cannot be prevented by the steel plate inspection machine. The third problem is that it is difficult for the steel plate inspection machine to detect the roughness of the steel plate hole wall, which depends on two factors: the resolution and magnification of the steel plate inspection machine's camera. The camera magnification is insufficient, and it cannot detect the burrs and foreign objects remaining on the hole wall of the steel plate; Another factor is the resolution of the camera, one side of the light is received by the camera through the opening, and the steel plate inspection machine with insufficient resolution cannot effectively catch the burr. The steel plate feeding inspection platform fixes the microscope lens through a simple gantry and can move in the X-Y direction, with the assistance of the bottom light, observe the quality of the steel plate opening, measure the size of the hole and the roughness of the hole wall. The ability to measure the roughness of the hole wall depends on the configuration of the microscope lens, the optical magnification of the lens configuration varies from 50X to 500X, and the common maximum magnification of 100X 3D microscope can clearly display most of the hole defects, effectively assisting industry colleagues to prevent the use of steel plates with poor hole opening. Figure 1.2.1 - Defects found in the incoming inspection of the steel plate. The thickness measurement of steel plate cannot be handled by the steel plate feeding inspection platform, especially the thickness problem of stepped steel plate has become a pain point in the current industry. In the smartphone industry, for example, the commonly used 80μm thick steel plate is locally thickened to 100μm to increase the local paste solderthickness, but in fact, the thickness of the mesh plate delivered by the steel plate manufacturer seriously deviates from the required thickness. The author has assisted enterprises to deal with the problem of less tin in solder joints of a product, the original 80μm mesh plate solder amount is too small, and after optimizing the first version of the local thickened steel mesh, the use results have not been significantly improved. The author did a slice test on this stencil, and the measured thickness of the stencil did not meet the standard at all, Figure 1.2.2 - Measured thickness of the staircase stencil. Such a deviation of the thickness value of the mesh plate cancels out the improvement countermeasures of the process personnel, and makes the countermeasures of the process personnel ineffective or even loses the judgment direction. When colleagues in the industry encounter similar problems, it is recommended to directly slice and confirm to avoid the continuous troubles caused by inaccurate measurements.

(3) PCB incoming inspection technology PCB incoming inspection includes four categories: dimensional measurement, solderability measurement, heat resistance characteristic measurement, and electrical characteristic measurement, each type of testing technology is different, and the equipment used is also different.

1.PCB Dimension Measurement PCB dimension measurement includes pad size, through hole size, outline size, position size, thickness size, etc. Among them, the pad size, through hole size, overall dimension, and position size use two-dimensional measuring equipment; PCB bending, twisting size using three-dimensional measuring equipment or dial gauge, plug gauge, etc.; PCB solder mask thickness, plating thickness, hole copper thickness, line width and thickness, etc., are measured using a film thickness tester or making slices. For example, if the left side of a product deviates from the left side and the right side deviates from the right side during the solder paste printing process, which is the true cause of the layer abnormality, it is necessary to use the second element to measure the distance between the left and right pads of the PCB, or measure the distance of the Fiducial mark on the left and right sides, and compare the measured value with the PCB design value to determine whether the printing deviation is caused by the expansion and contraction of the PCB.

2.PCB Solderability Measurement There are several test schemes for printed circuit board solderability testing: solder balance experiment, small solder pot bleaching test, wave soldering bleaching test, and solder paste printing test.

(1) Solder balance test Solder balance test is the only quantified test method among all solderability tests, and it is also the most accurate solderability test. The solder balance test uses an ultra-precision solder balance, the sample to be tested is clamped with a fixture and suspended on the precision balance, and the buoyancy and wetting force (solder creep force) will be generated when the test sample comes into contact with molten solder, and the solderability of the sample to be tested is determined by calculating the magnitude and occurrence time of buoyancy and wetting force. Figure 1.3.2-1 Solder Balance Tester and Measured Wettability Curve for Solder Balance Test. The wetting balance method can accurately determine the solderability of the PCB, but due to the size of the test platform, it is not possible to do the whole board test.

(2) Small tin pot bleaching test Small tin pot bleaching test is a commonly used solderability test method in PCB board factories, and its basic standards and operations refer to J-STD-003 and IPC-TM-650 Section 2.1.1. It should be noted that the pretreatment of PCB solderability test has a direct logical relationship with the test results: the double-sided soldering process is commonly used in the industry at present, so the PCB tin bleaching test needs to be aged twice before the Reflow process and then resided at room temperature for 24 hours, and then the tin bleaching test is done to simulate the actual production conditions for the PCB solderability requirements. This is the case with wave soldering every other day after the production of double-sided SMT is completed. The small tin pot bleaching test is to take the standard fluxafter the PCB has been pre-treated, immerse it in the molten small tin pot for 3 seconds, take it out vertically, and observe the wetting of the PCB pad and through-hole solder. This test can be completed without specialized equipment, with only a small tin pot required, and is an economical test solution that is simple to operate, highly efficient, and focused on low cost. Figure 1.3.2-2 Small tin pot bleaching test.

(3) Wave soldering bleaching test Wave soldering bleaching test is a commonly used test scheme in PCBA factories, which is closest to the actual production situation. The pretreatment of the PCB is the same as the small tin pot bleaching experiment, the difference is that the wave soldering bleaching test is to send the pretreated board to the wave soldering production line, use the carrier to fasten the PCB, and directly send the wave soldering spraying flux, preheating, and tin wave without inserting components, and observe the PCB pad soldering wetting results after the furnace to determine its solderability. This test does not require any special equipment, nor does it require any professional assistance, it can be completed with the normal operation of production, and is a commonly used testing scheme in PCBA factories.

(4) Solder paste printing test The solder paste printing scheme to determine the solderability of the PCB is to reside the PCB in the room temperature environment for 24 hours after the bare board has passed through Reflow according to the actual production needs, and then use the corresponding steel plate to print the solder paste, and directly pass through the Reflow without placing the components, and observe the solder wetting status on the pad after the furnace, that is, the paste solder board does not mount the components directly through the reflow oven to observe the tin quality on the pad, which is an effective solution for continuous monitoring of PCB solderability during continuous production of mass production mode enterprises.

1.PCB heat resistance characteristics measurement PCB heat resistance characteristics testing is also known as heat resistance dissolution test, tin bleaching test, the difference is that the temperature of the tin bath used in this test is 288oC, the PCB is immersed in the solder bath for 10 seconds and then taken out, to observe whether the PCB has solder mask discoloration, delamination, bulging, silk screen falling off and other phenomena. The purpose of this experiment is to identify whether the high temperature resistance characteristics of the PCB meet the production requirements, and avoid the occurrence of product scrap due to PCB heating in the actual production process.

2.Electrical Characteristic Measurement PCB electrical characteristic testing includes line impedance test (line impedance tester), line insulation impedance test, signal attenuation, signal delay test, line withstand voltage and current test, etc., which requires the use of oscilloscope, power simulator and other equipment. Tg point test, Td point test, hardness test, CTE test, etc. of PCB board belong to failure analysis or new product selection and identification test, and are not included in the incoming inspection.

Chip incoming inspection technology

The commonly used items for incoming inspection of chip components include but are not limited to the following: appearance size measurement (two-dimensional measuring equipment, micrometer), end electrode size measurement (two-dimensional measurement equipment), resistance measurement (LCR Meter), capacitance measurement (LCR meter), inductance measurement (high-frequency LCR meter), end electrode solderability test (small solder pot, solder balance), component body damage test (precision pressure gauge), component end electrode bending test (precision pressure gauge), End electrode peel strength test (push-pull force meter), component withstand voltage test (power simulator), salt spray test, comprehensive gas test, etc.

Appearance size measurement and solderability measurement are often used when the component placement and welding are abnormal, and whether the layer is an abnormal incoming material causes the appearance to be poor. If the capacitance value is abnormal or breakdown, the commonly tested item is surge test: apply a momentary voltage or current to the capacitor to evaluate its anti-burn and breakdown ability. Resistance feed test is often used to identify changes in the electrical characteristics of the resistor when the vulcanization fails or when the resistance value deviates.

IC component incoming inspection technology

The common inspection contents of IC component feeding include: appearance inspection (stereo microscope), solderability test (small solder pot, solder balance), pin coplanarity test (common plane tester, three-dimensional), coating thickness test (slice test), electrical characteristic test (oscilloscope, power simulator), size test (micrometer, two-dimensional), etc. Most of the IC components are MSD controlled devices, and the incoming inspection also needs to check whether the packaging is damaged and whether the moisture sensitive card is discolored. It needs to be mentioned that there is an unqualified moisture sensitive card on the market, which is stored at room temperature for a long time and does not change color, and the use of this kind of moisture sensitive card will mislead industry colleagues, and the IC that has been damp will be directly used for soldering, and the probability of high temperature delamination failure will be greatly increased. Figure 1.5 - A moisture sensitive card that never changes color.

Component solderability inspection technology

Component solderability test is a common quality specification for every device that needs to be soldered, whether it is surface-mount soldering components, through-hole plug-in soldering devices, assembly test structural parts, wiring harnesses, etc., all need to maintain certain solderability characteristics. The commonly used materials for the solderable terminals of the components are copper, white copper, phosphor bronze, #42, Cova alloy, stainless steel, aluminum-magnesium alloy, tinplate, etc., and most of the metals will undergo oxidation reaction when stored in the air for a long time, which affects the weldability.

The commonly used protective layer materials in the industry are gold, silver, nickel, tin, zinc, etc., because gold, silver, tin and other materials will diffuse with the copper substrate, nickel is generally used as a barrier layer, but nickel itself is also prone to oxidation reaction, so it is often nickel plated on the substrate, and then tin, gold, silver, etc. are plated as the surface protective layer. Aluminum, aluminum-magnesium alloy, stainless steel, iron and other materials can not react directly with soldering for welding, and the commonly used solution is to plate nickel on the non-solderable base material, and then give the nickel layer top layer protection (gold, silver, tin) to ensure the weldability of parts. Whether it is electronic components, metal parts, non-metal parts, wiring harnesses, fasteners, etc.,

Where welding is required, incoming inspection and testing of its weldability are necessary control items. The production line often uses soldering iron and tin wire to make preliminary judgments to determine the solderability of parts; IQC incoming inspection commonly uses a small tin pot dipping test to determine the solderability of parts; The most commonly used method is the solder balance method to accurately determine the solderability of parts. The working mechanism and practical application interpretation of weldability balances are elaborated in the author's book "Product Failure Analysis Mechanism and Preventive Countermeasures", which can be referred to by interested colleagues.

Connector temperature resistance testing technology

From the perspective of welding, connectors can be divided into three categories: pure surface mount soldering connectors, surface mount + through-hole reflow soldering connectors, and through-hole plug-in soldering connectors (wave soldering, selective soldering, manual soldering, and Mini soldering), and the types of connectors are distinguished in Figure 1.7-1. Both Type 1 and Type 2 connectors need to be reflowed, and their body materials must meet the requirements of high-temperature soldering.

Generally, it is required that the plastic material of the lead-made process connector body has a temperature resistance of ≥260oC, and the plastic material of the lead-free process connector body has a temperature resistance of ≥280oC. It should be noted that this temperature is the Reflow set temperature, that is, the hot air temperature, not the solder joint temperature. Some products have a large heat capacity, the reflow oven set temperature and the measured solder joint temperature are quite different, the industry commonly uses to pull up the set temperature to ensure that the solder joint is tin melted normally, the set temperature of the set temperature also means that the hot air temperature blown into the furnace by Reflow is high, if the temperature resistance of the connector body material is insufficient, there will be abnormal melting, deformation, distortion and other abnormalities of the plastic body. IQC incoming inspection can be used to qualify this characteristic using teppanyaki (heating platform), small tin pot, Reflow, heat gun, etc. SMT connectors (and) are less likely to appear in the body material is not temperature resistant to cause abnormal phenomena, common is the body discoloration, such as white connector after the furnace yellowing, body bending, such as surface mount connector after the furnace warping, virtual welding, etc., the incoming inspection needs to be included in the temperature resistance detection control items.

The common abnormality caused by the insufficient temperature resistance of the connector body in the industry is the melting and deformation of the plastic material of the body in the pure through-hole insertion soldering process of wave soldering, selective soldering, manual soldering, and mini soldering, and the terminal collapse and distortion of the body. The evaluation of the temperature resistance knowledge and ability of the through-hole plug-in welding device body is the responsibility of the research and development of CE, and some companies only pay attention to the electrical functions of the parts, ignoring or not having the knowledge of the temperature resistance evaluation of the parts, and the plastic body melts in the actual production process of the selected devices, which affects the normal production quality. The most common verification conditions are 280oC small solder pot temperature, connector terminal insertion for 5 seconds, and terminal insertion depth of 2.5mm. Figure 1.7-2 Wave soldering connector plastic body melting.

Incoming inspection technology of structural parts

The common contents of incoming inspection of structural parts are: dimensional measurement, matching measurement, hardness measurement, toughness measurement, weldability measurement, coating thickness measurement, temperature resistance testing, friction resistance testing, etc. The size measurement of structural parts uses two-dimensional, vernier caliper, micrometer, three-dimensional and other testing equipment and tools. Physical matching detection is commonly used in matching measurement, that is, the use of PCB or corresponding plugs, sockets, etc. The friction resistance test generally uses physical plugging or simulated plugging to test the contact reliability of repeated plugging of connectors, or uses a pencil with a specified hardness to sharpen and poke the test. The structural parts are deformed by heat during welding, which will lead to dimensional deformation or relative position changes, which is also a key project in the industry, that is, the detection of thermal deformation characteristics.

Harness incoming inspection technology

The contents of the wire harness feeding inspection include the following common items: wire harness size, core cross-sectional area, wire core damage ratio, wire stripping length, terminal connection quality, wire harness tin quality, terminal locking structure, wire harness insulation rubber temperature resistance, insulation rubber corrosion resistance, wire harness bending resistance, wire harness weldability. For example, when a wiring harness is inserted and welded, there is always a wiring harness that does not go out of the foot phenomenon (also known as over-welding), and the inspection of the wiring harness finds that there is an inconsistent length of the wiring harness, and the length of the wiring harness is inconsistent in Figure 1.9-1. Such defects should be effectively intercepted in the IQC incoming inspection to avoid abnormal production lines. Fig. 1.9-2 wire harness stripping damage, Fig. 1.9-3 wire harness tin immersion is unqualified.

Chemical Incoming Inspection Techniques

Most enterprises adopt inspection-free treatment for chemical feeding, the reason is that the chemical incoming inspection operation is relatively complex and requires the assistance of instruments and corresponding chemicals. For example, acid-base titration test requires a titrator, standard titration solution, etc., and also needs to be reported to the control unit for the record. Generally, there are no chemical incoming inspection items in factories, and some factories measure simple items such as chemical specific gravity, PH value, halogen content, and moisture content. The industry does not require PCBA factories to do IQC incoming inspection of chemicals, but excellent factories will set up laboratories and laboratories with chemical testing capabilities.

Tin bar & tin wire incoming inspection technology, etc

The incoming inspection of tin bars mainly tests its composition, most factories use spark discharge testers to check the composition of tin bars, and the more sophisticated test scheme is the ICP chemical test method to detect the alloy composition and impurity content of tin bars. In addition to the alloy composition test, it is also necessary to test the flux content, halogen content, fin frying characteristics test, flux corrosivity test, wire diameter test, etc. The flux content test scheme is simply to melt a certain amount of tin wire into a ball, use a solvent to clean off the flux, and weigh the solder quality after drying, so as to calculate the flux content. The flux content affects the soldering quality and the use effect of solder wire, which is one of the indispensable contents of solder wire evaluation. There are two types of tin wire halogen content test, qualitative test and quantitative test, the qualitative test is used to distinguish whether the halogen content of tin wire exceeds 1000ppm, and the quantitative test needs to be combined with the titration test to calculate the accurate halogen content. Qualitative testing, such as silver chromate test strips, can be used to test extracts for simple and fast determination of halogens. It should be noted that the definition of halogen-free in the industry is halogen content < 1000ppm, and halogen-free at all is zero halogen. The basic operation of the tin frying test is to melt a certain length of tin wire such as 2.5cm into the soldering iron tip, the temperature of the soldering iron tip is 350oC, the temperature of the soldering iron tip is 350oC, the lead-free is 380oC, and the height of the soldering iron tip from the desktop is 5cm. Lay clean white paper on the tabletop, and observe the number and size of tin beads on the white paper after tin melting, so as to evaluate the probability of forming tin beads during the use of tin wire welding. The solder wire diameter test can be accurately determined using vernier calipers or two-dimensional elements. The corrosivity test of tin wire flux needs to be sent to the laboratory for execution, and the commonly used test items are copper mirror test, copper sheet test, SIR, etc.

Chip incoming inspection technology

The commonly used items for incoming inspection of chip components include but are not limited to the following: appearance size measurement (two-dimensional measuring equipment, micrometer), end electrode size measurement (two-dimensional measurement equipment), resistance measurement (LCR Meter), capacitance measurement (LCR meter), inductance measurement (high-frequency LCR meter), end electrode solderability test (small solder pot, solder balance), component body damage test (precision pressure gauge), component end electrode bending test (precision pressure gauge), End electrode peel strength test (push-pull force meter), component withstand voltage test (power simulator), salt spray test, comprehensive gas test, etc.

The common items of chip component incoming inspection include but are not limited to: appearance size measurement (two-dimensional measuring equipment, micrometer), end electrode size measurement (two-dimensional measurement equipment), resistance measurement (LCR Meter), capacitance measurement (LCR Meter), inductance measurement (high-frequency LCR meter), end electrode solderability test (small tin pot, solder balance), component body damage test (precision pressure gauge), component end electrode bending test (precision pressure gauge), End electrode peel strength test (push-pull force meter), component withstand voltage test (power simulator), salt spray test, comprehensive gas test, etc.

IC component incoming inspection technology

When there is an abnormality in component placement and welding, the appearance size measurement and solderability measurement are often carried out to distinguish whether the defective appearance is caused by the abnormality of the incoming material. For the case of abnormal capacitance or breakdown, the common test item is surge test, that is, the instantaneous voltage or current is applied to the capacitor to evaluate its anti-burning and breakdown ability. Resistance feed tests are often used to identify changes in the electrical characteristics of resistors in the event of vulcanization failure or resistance deviation.

Component solderability inspection technology

Because gold, silver, tin and other materials will diffuse with copper substrates, nickel is generally used as a barrier layer, but nickel itself is also prone to oxidation reaction, so it is often nickel plated on the substrate, and then tin, gold, silver, etc. as the surface protective layer. Aluminum, aluminum-magnesium alloy, stainless steel, iron and other materials can not react directly with soldering for welding, and the commonly used solution is to plate nickel on the non-solderable base material, and then give the nickel layer top layer protection (gold, silver, tin) to ensure the weldability of parts. Whether it is electronic components, metal parts, non-metal parts, wiring harnesses, fasteners, etc.,

The common inspection contents of IC component feeding include: appearance inspection (stereo microscope), solderability test (small solder pot, solder balance), pin coplanarity test (common plane tester, three-dimensional), coating thickness test (slice test), electrical characteristic test (oscilloscope, power simulator), size test (micrometer, two-dimensional), etc. Most of the IC components belong to MSD controlled devices, and it is also necessary to check whether the packaging is damaged and whether the moisture sensitive card is discolored during the incoming inspection. It should be pointed out that there is an unqualified moisture sensitive card on the market, which does not change color when stored at room temperature for a long time, and the use of this moisture sensitive card will mislead peers and directly use the wet IC for welding, thereby greatly increasing the probability of high temperature delamination failure. Connector temperature resistance testing technology

The component solderability inspection technology generally requires a temperature resistance of ≥260oC for the plastic material of the lead-made process connector body, and a temperature resistance of ≥280oC for the plastic material of the lead-free process connector body. It should be noted that this temperature is the Reflow set temperature, that is, the hot air temperature, not the solder joint temperature. Some products have a large heat capacity, the reflow oven set temperature and the measured solder joint temperature are quite different, the industry commonly uses to pull up the set temperature to ensure that the solder joint is tin melted normally, the set temperature of the set temperature also means that the hot air temperature blown into the furnace by Reflow is high, if the temperature resistance of the connector body material is insufficient, there will be abnormal melting, deformation, distortion and other abnormalities of the plastic body. IQC incoming inspection can be used to qualify this characteristic using teppanyaki (heating platform), small tin pot, Reflow, heat gun, etc. SMT connectors (and) are less likely to appear in the body material is not temperature resistant to cause abnormal phenomena, common is the body discoloration, such as white connector after the furnace yellowing, body bending, such as surface mount connector after the furnace warping, virtual welding, etc., the incoming inspection needs to be included in the temperature resistance detection control items.

Component solderability testing is a common quality specification for all devices that need to be soldered, whether it is surface-mount soldering components, through-hole plug-in soldering devices, assembling test structural parts or wiring harnesses, etc., they need to maintain certain solderability characteristics. The commonly used materials for component solderable terminals are copper, white copper, phosphor bronze, #42, Cova alloy, stainless steel, aluminum-magnesium alloy, tinplate, etc., and most metals will undergo oxidation reaction when exposed to air for a long time, which will affect the weldability.

Incoming inspection technology of structural parts

The commonly used protective layer materials in the industry are gold, silver, nickel, tin, zinc, etc., because gold, silver, tin and other materials will diffuse with the copper substrate, so nickel is generally used as a barrier layer, but nickel itself is also prone to oxidation reaction, so it is often nickel plated on the substrate, and then tin, gold, silver, etc. are plated as the surface protective layer. Aluminum, aluminum-magnesium alloy, stainless steel, iron and other materials cannot be welded directly with solder, and the common solution is to plate nickel on the non-solderable substrate, and then make the top layer protection (gold, silver, tin) on the nickel layer to ensure the weldability of the parts. Whether it is electronic components, metal parts, non-metallic parts, wiring harnesses, fasteners, etc., as long as welding is required, incoming inspection to test its weldability is a necessary control item. The production line often uses soldering iron and tin wire to make preliminary judgments to determine the solderability of parts; IQC incoming inspection commonly uses a small tin pot dipping test to determine the solderability of parts; The most common method used to accurately determine the solderability of a part is still the solder balance method. The working mechanism and practical application interpretation of solder balances are elaborated in the author's book "Product Failure Analysis Mechanism and Preventive Countermeasures", which can be referred to by interested colleagues.

Chemical Incoming Inspection Techniques

From the perspective of welding, connectors can be divided into three categories: pure surface mount soldering connectors, surface mount + through-hole reflow soldering connectors, through-hole plug-in soldering connectors (wave soldering, selective soldering, manual soldering, Mini soldering), the first and second types of connectors need to go through Reflow, and their body materials must meet the needs of high-temperature soldering.

Tin bar & tin wire incoming inspection technology, etc

Generally, it is required that the plastic material of the lead-made process connector body has a temperature resistance of ≥ 260°C, and the plastic material of the lead-free process connector body has a temperature resistance of ≥280°C. It should be noted that this temperature is the Reflow set temperature, which is the hot air temperature, not the solder joint temperature. Some products have a large heat capacity, the reflow oven set temperature and the measured solder joint temperature difference is large, the industry commonly uses the method of pulling up the set temperature to ensure that the solder joint is soldered normally, the set temperature means that the hot air temperature blown into the furnace by Reflow is high, if the temperature resistance of the connector body material is insufficient, there will be abnormal situations such as melting, deformation, and distortion of the plastic body. IQC incoming inspection can qualify this feature using teppanyaki (heating platform), small tin pot, Reflow, heat gun, etc. SMT connectors are less likely to be abnormal due to the temperature resistance of the body material, the common is the body discoloration, such as the white connector after the furnace yellowing, the body bending, such as the surface mount connector after the furnace warping affects the virtual soldering, etc., the temperature resistance test needs to be included in the control items during the feed inspection.