GB/T 2424.17-1995 Environmental testing guidelines for electrical and electronic products - Soldering tests
Some standard content:
National Standard of the People's Republic of China
Environmental testing for electric and electronic products
Guidance on soldering test
1 Subject content and scope of application
GB/T 2424.17---1995
Replaces GB2424.17---82
This standard provides background information on soldering test for the compilers and testers of electrical and electronic component specifications. This standard applies to electrical and electronic components connected by soldering process. 2 Reference standards
GB2423.28 Basic environmental testing procedures for electric and electronic products Test T: Soldering test method GB4677.10 Test method for solderability of printed boards 3 Basic conditions for soldering
The difficulty and reliability of soldering connection depends on the following three conditions: a. Connection design: including the shape, size, composition and assembly method of the selected metal parts to be connected; b. Wetting of the surface of the metal parts to be connected; C. Conditions used for soldering connection, including temperature, time, flux, solder alloy, equipment, etc. The selection of conditions a and c involves the manufacturer of the equipment or components, who must understand the importance of each condition and the limits of their variation. Condition b is in most cases determined by the component manufacturer, and improper handling or storage by the equipment manufacturer also has an impact. The equipment manufacturer must make provisions for surface wettability according to conditions a and c regardless of the degree of accuracy. In order to ensure the reliability of interconnection in complex equipment, components must have satisfactory surface quality. The responsibilities between component manufacturers and equipment manufacturers are often overlapping, so it is necessary to make a clear provision for the wettability of component leads or, more generally, the solderability of components. 4 Solderability of components and wettability of their leads It is not enough for electronic components to have only one lead that can be wetted by molten solder and is suitable for soldering. In order to withstand batch soldering operations, the following three requirements must be met.
a. Must have good heat transfer properties, at least enough to withstand a sufficiently high temperature above the liquidus of the solder alloy used and maintain it for a long enough time to produce wetting;
h. Must withstand the thermal stress during soldering (including rework and repair with iron) without short-term or long-term changes; c. Must withstand the mechanical and chemical stress during the cleaning process to remove residual flux without short-term or long-term damage. This guide does not emphasize cleaning.
Some electronic components cannot be subjected to batch soldering operations because they cannot withstand one or several stresses related to the process operation. Such components include: mechanical parts containing lubricants, such as switches; non-sealed components that are sensitive to contamination, such as relays, potentiometers; or plastic materials with poor heat resistance, such as capacitors with thermoplastic dielectrics. Approved by the State Administration of Technical Supervision on January 27, 1995, and implemented on August 1, 1995
GB/T2424.17—1995
For this reason, it is necessary to distinguish between the two concepts of component solderability and terminal wettability. Component solderability refers to the overall adaptability to industrial soldering, while terminal wettability refers only to the ease with which the terminal surface is wetted by solder. However, these two concepts are often confused in daily discourse, and this confusion will hinder the normal operation of production. In addition, the fact that a component is not suitable for soldering under generally specified conditions (see Chapter 6) does not mean that its terminals cannot be soldered to a printed circuit board or other brackets. This means that special measures should be taken according to its characteristics, such as when the component has a heat-sensitive isolation layer or is incompatible with some or all solvents. Only poor terminal wettability will hinder the soldering application of the component. This performance is very important, and of course it does not exclude the consideration of other performances. The standard tests referred to here are tests that simulate the effects of some of these conditions. Appropriate selections are made from this set of tests, including electrical and mechanical measurements, and allow the person concerned to answer the following question: Is this component solderable by the usual methods used in electronics? This is one of the questions that the equipment manufacturer must answer before putting a component on a soldering line. The principles of each standard test and the information it provides are specified in Chapter 5. The compiler of component specifications can have good reasons to select the necessary test items in this way to determine the characteristics of the component during the soldering process.
Similarly, the tester should correctly evaluate the information obtained from the test. 5 Arrangement of Solderability Tests in Environmental Tests 5.1 Effect of Test Sequence on Solderability Tests In the previous chapter, the exact meaning of the tests was analyzed to show how they can be used to answer the question "Is this component solderable in normal methods in practice?"
Of the many characteristics of a component, performance, ruggedness, expected life, etc., solderability is only one of them, and an important one.
If the solderability test specification does not specifically specify the test sequence, the order of solderability tests must be carefully arranged in a test sequence, because the various conditions that the component was subjected to during the previous test may affect the results of the solderability test. Therefore, improper arrangement may give erroneous results and may affect the results of other component characteristic tests. For example:
In a test procedure, long-term humidity and heat or corrosion tests are performed before wettability tests. Although the wettability of the component is satisfactory when received, the component may still be rejected. In fact, various electronic components are usually subjected to humidity and heat and salt spray tests after being soldered into the device.
On the contrary, in order to correctly simulate the component being mounted on the printed board, if the soldering heat resistance test is placed before the lead strength test, then the sealing failure caused by the lead strength test will not be affected by the thermal shock. In fact, the cumulative mechanical and chemical effects can confirm the component failure.
5.2 The general principles for arranging the test sequence are as follows: a: Non-destructive tests and tests such as accelerated aging tests (see Chapter 8) performed according to specified requirements can be performed before wettability tests;
b. Soldering heat resistance tests should be independent of long-term operation tests, and all necessary precautions should be taken, such as the use of heat shielding; c. Before conducting climatic tests, it should be considered whether flux residues need to be cleaned off, and before other mechanical and chemical tests, it must also be considered whether active flux residues need to be removed. 6 Solderability Tests
In the electronics industry, soldering conditions vary greatly, but it is usually not necessary to use different types of components to meet different installation conditions. Industrial welding conditions can be divided into several corresponding narrow ranges. The ranges listed in Table 1 are widely used.
Process temperature range
Heat exposure duration
GB/T2424.17--1995
Sn-Pb with approximate eutectic composition
Soldering iron
230300℃
Trough soldering or wave soldering230~260℃
Vapor phase soldering
Infrared soldering
Soldering iron
210～260℃
200～280℃
Trough soldering or wave soldering3~55
Vapor phase soldering
Infrared soldering
20~60 s
30~60s
These conditions are determined based on experience between high stress and low stress. High stress refers to high temperature or long time. The advantage is that it can improve wettability but easily damage components. Low stress refers to short time or temperature close to the melting point of solder. The advantage is that components are not easily damaged but are not easy to weld or the welding quality is poor (cold connection). After comprehensive consideration, the standard test conditions are: solderability test temperature is 235℃, soldering heat resistance test temperature is 260℃, and the soldering time also takes these factors into consideration, so that a component can withstand the stress range that may be encountered in the normal assembly process after passing the standard test.
The changes in the same batch of components with the same process and between component batches show that things are complicated. This means that the test results obtained on one component cannot be used as a typical example of other components in the same batch or other batches of components. Since the test takes a lot of time and may be destructive, the results of one batch or several batches can only be used as a statistical evaluation. Specification compilers and users must remember that statistical analysis of component solderability test results is an important task. And conduct tests accordingly.
GB2423.28 only specifies how the test is to be carried out and does not include statistical analysis. Statistical analysis of the test results is the subject of a detailed specification.
Statistical treatment is relevant to the applicability of the test results and, in particular, to the specified confidence level (see Clause 9). For the soldering heat test, it is appropriate to use an active flux to produce rapid wetting, which ensures that the test component is heated as quickly as possible.
The discussion on the choice of solder and temperature also applies to the soldering heat test. When testing components with large thermal capacity, it should be ensured that the temperature does not fall below 40°C above the liquidus of the solder. The solder bath of Test Method 1 should be of sufficient size to ensure that the temperature can be effectively maintained. The test is not intended to simulate or determine the effects of accidental mechanical stress caused by the soldering process. The test may cause damage or destruction to the test specimens. This should be borne in mind when deciding to perform climatic and mechanical sequence tests. 7 Wettability test
7.1 General principles
The purpose of the test is to combine the component leads with the solder under controlled conditions so that the quality of wetting can be determined according to the specified standards. Basically, the soldering time test is to estimate the time required for the contact angle at all points on the solder boundary to drop to a low angle uniformly. In some tests, it is only assessed by visual inspection. In other tests, the time is measured. A completely quantitative test is to measure the change in the surface tension of the solder applied to the sample over time. Under certain circumstances, the contact angle may increase again by extending the immersion time, and the solder will shrink from the sample surface. This phenomenon is known as weak wetting. Some test methods provide weak wetting tests. Where weak wetting is suspected, the relevant specifications should require this test to be included. 7.1.1 Various test methods and their scope of application 603
GB/T 2424.17-1995
The various test methods and their scope of application are shown in Table 2! Table 2
Test method
Solder slot test
Soldering iron test
Solder ball test
Rotary diffusion test
Wetting weighing test
Diffusion soldering test
Micro wetting weighing test
7.1.2 Test procedure in type test
Applicable to component leads, qualitative
Scope of application
Applicable to leads that are not suitable for testing by other methods, qualitative Applicable to round leads, measuring wetting time Applicable to printed board samples, measuring wetting degree and weak wetting Applicable to leads with regular cross-section, measuring wetting force and time, qualitative Applicable to surface mount components, qualitative
Applicable to surface mount components, qualitative
This standard also gives the principles for the application of accelerated aging tests. Specification writers must note that the test sequence in the type test should be arranged as follows: Soldering should not be performed before the wettability test, such as for initial measurements. a.
Aging that may affect wettability, such as preconditioning at elevated temperatures, should not be performed unless required by the component specification. b.
|The terminal surface should not be damaged during any preconditioning process. c.
Therefore, the wettability test must be performed first in any test sequence. 7.1.3 Precautions
The following precautions apply to all solderability test methods: The test must be performed under no ventilation or protective ventilation conditions. a.
. To avoid contamination of the sample during handling, it is recommended to use a soldering iron. If the leads need to be straightened before testing, this should be done in a manner that does not contaminate or scratch the sample. c.
7.2 Solder Bath Test
There are two types of this test, one for wire and stick terminals and one for printed circuit boards. The solder bath should be sized so that the solder temperature does not drop significantly during the flooding process. The procedure in Method 1 is quite simple and its application would be limited if it were specified in too much detail. This method can be used, for example, for skewer terminals which are not suitable for testing by the solder ball method due to their shape and are designed to be soldered by solder baths. In printed circuit board testing, there are no geometry-related issues and therefore more detailed specifications can be made. The immersion depth of the printed board should be strictly limited to ensure that the solder introduced into the plated hole is caused by wetting and not by liquid pressure. 7.3 Soldering Iron Test
This method is reserved for evaluating the wettability of terminals that cannot be tested by the solder ball or solder bath method. Solderable enameled wire is a typical example for which the temperatures of the other methods are too low. Some skewer terminals that are not suitable for solder bath testing can only be tested by soldering iron.
The test is somewhat sensitive to temperature and the test result is related to the heat capacity of the component. These factors are of course also applicable to soldering production, but the active flux commonly used in soldering production, which can greatly shorten the soldering time, should be eliminated when formulating component specifications. The test is rapid, qualitative and discriminating. If desired, the wettability can be tested at multiple points on the terminal. 7.4 Solder ball test
7.4.1 Solder ball test for wire and round cross-section terminals This test is applicable to wire with a diameter of 0.1 to 1.2 mm. The sample to be tested is dipped in flux and then placed horizontally so that the molten solder ball is evenly divided. The time required for the solder ball to enclose the sample is recorded. The height of the solder ball is controlled by the weight of the solder ball. The height of the solder ball should be controlled so that the solder ball will not enclose above the sample under non-wetting conditions. The solder ball is placed on a pure iron cylinder with a diameter of 4mm. The pure iron is covered with non-wetting aluminum. The aluminum can also be used to stabilize the temperature of the pure iron cylinder.
The upper surface of the pure iron cylinder must be kept well wetted with solder. When the test is completed and the heating is stopped, the heating block must be cooled together with the solder ball on it to prevent oxidation or poor wetting of the pure iron surface. In case of dispute, it should be checked that the weight of the solder ball used must be within ±10% of the nominal weight. During the test, the pure iron surface must be kept very clean, the flux in the container must be sealed to prevent the solvent from evaporating and thickening, and the amount of flux applied should not be too much to cause the temperature of the solder ball to drop for a long time. Each solder ball must be clean and bright, and the solder ball must be selected to fit the lead diameter. The lead must correctly divide the solder ball equally. If it is obviously off the center, the result must be invalidated.
It is useful to measure the time interval with an electronic timing device which automatically starts when the terminal bisects the ball. The timing device can be stopped manually by observing the ball encapsulating the lead or automatically by the timing probe above the specimen contacting the ball. If the speed is too slow, the start time will be inaccurate because the height of the ball varies from 0.9 mm (50 mg) to 2.3 mm (200 mg) (using a 4 mm core). When the timing is done manually, there will be errors in the encapsulation time due to the different reaction speeds of the operators, but these errors are not important in acceptance tests.
7.4.2 Test of Solder Balls with Non-Circular Cross-Sections
This test is suitable for terminals with any convex cross-sectional shape, but is mainly used for rectangular cross-sections. Terminals formed by stamping may have burrs, which will form pits in the cross-section if their length exceeds 1/10 of the thickness. 7.5 Rotary Dipping Test
See GB4677.10
7.6 Wetting Weighing Test
This test can provide a function of the wetting force changing with time during the entire wetting process, thereby making a quantitative evaluation. The component specification can select a specified degree of wetting as the acceptance level. 7.7 Solderability of Surface Mount Components, Solvent Resistance and Soldering Heat Resistance Test of Metallization Layer 7.7.1 Overview
Originally, solderability tests hope to obtain quantitative objective results rather than qualitative subjective results. This specification is used for qualitative inspection of surface mount components as a transitional method before quantitative test procedures. 7.7.2 Limitations
For samples plated with pure tin terminals, the results obtained by immersion tests at 235°C may not be consistent with the performance under assembly conditions, such as using vapor phase soldering below the melting point of tin. Tests at 215°C are used to solve this problem. 7.7.3 Selection of severity Www.bzxZ.net
7.7.3.1 Immersion at 235°C for 2 seconds and at 260°C for 10 seconds These conditions are conventional conditions for testing wettability and resistance to soldering heat, respectively. It should be noted that since wettability is evaluated after dipping, this method cannot measure the wetting rate, but it can indicate whether an appropriate degree of wetting can be achieved within the specified time. The relevant specifications may specify a lower level of resistance to soldering heat with an immersion time of 5 seconds. 7.7.3.2 Immersion at 215°C for 3 seconds This condition is a test carried out at a relatively low temperature and is suitable for vapor phase welding, because the results obtained at 235°C do not need to have any correlation with the results at 215°C. Since the wetting reaction on an already wetted surface is expected to be slower, a longer time is specified. There is not always a definite relationship between slot welding and vapor phase welding. 7.7.3.3 Dipping at 260°C for 30s During the wave soldering process, the rate of melting of the metallization layer is much greater than that during static dipping. After wave soldering, reflow soldering or vapor phase soldering, it may be necessary to use a soldering iron for repair and rework. Therefore, a longer dipping time at a higher temperature is specified to test the dissolution resistance of the metallization layer in the molten solder.
GB/T2424.171995
The relevant specifications may specify a lower level of dissolution resistance test with a dipping time of 10s or 20s. 7.7.3.4 Dipping posture
When testing resistance to soldering heat, if a flat sample of a certain size (such as a ceramic chip carrier) is dipped with the sealing surface in a vertical state, it will not be able to withstand the thermal gradient generated on its thickness during the actual soldering process. In this case, the specification compiler should choose posture B (suspended state). It is not desirable to use different dipping times for samples of different sizes. 8 Description of test conditions
8.1 Classification
Figure 1 shows the various parts and methods that make up test T and their relationship to each other. Test T
Test Ta
Solderability
Method 1A
Accelerated aging
Method 1
235±5℃
Weak wetting
260±5℃
Method 2
350±10℃
Test Tb
Resistance to soldering heat
Method 1B
350±10℃
Method 3
235±2℃
Method 2
350±10℃
Method 4
Wetting weighing
235℃
Weak wetting
Test Te
Printed board can Solderability
Accelerated aging
Reference GB4677.10
Weak wetting
Test Td
Solderability of surface mount devices Metallization layer Solvent resistance and resistance to soldering heat
Accelerated aging
215±3℃
235±5℃
260±5℃
Weak wetting
Method 1A (260℃ solder bath), Method 1B (350℃ solder bath) and Method 2 (350℃ soldering iron) are not a test method in themselves, but more of a simulation of climatic exposure prior to tests such as electrical properties and terminal strength. They do not include test procedures for resistance to mechanical stress during soldering.
8.2 Test material selection
8.2.1 Solder selection
The solder used for welding in electronic and electrical equipment is mostly a solder alloy of 60% tin and 40% lead, so all tests also use this solder. Experience shows that when the impurity content meets the requirements of Appendix B of GB2423.28, it will not affect the wetting ability of the solder. 606
8.2.2 Flux selection
GB/T2424.171995
The flux used for welding in electronic and electrical equipment is mostly rosin flux with activator (modified or natural). The role of the activator is to improve the wettability of the flux or increase the dissolution rate of the metal oxide layer. The activated flux can produce a very short welding time. They are generally patented products with undisclosed formulas. In order to avoid the difficulty of specifying the soldering time for each active flux and to include the worst case, we prefer to use non-activated rosin flux for soldering tests so that the soldering duration can be easily measured. The specified active flux is allowed only when soldering cannot be performed without the active flux. It must be emphasized that the active flux in the solderability specification does not necessarily represent the practicality of the product in production, nor does it guarantee that its residue is not corrosive.
The most commonly used flux is isopropyl alcohol rosin solution or alcohol rosin solution. The solder ball method test shows that the soldering time is not affected when the rosin weight ratio changes between 25% and 40%. Considering that the concentration increase caused by solvent evaporation during the test does not affect the test results, a concentration of 25% by weight is selected as the standard concentration.
8.3 Accelerated Aging Methods
8.3.1 Natural Aging
The effect of natural aging (storage before mounting on a printed circuit board) on the terminals depends mainly on three factors: a. the packaging form;
b. the natural environment in which the components are stored (temperature, relative humidity, atmospheric pollution, etc.); c. the characteristics of the materials and their coatings.
Accordingly, despite the same manufacturing process, different natural aging methods, such as diffuse oxidation, sulfidation, partial hydration or even significant corrosion, can change the wettability of the same coating. People have imagined that any precise change in surface wettability can be predicted. The research literature clearly shows that despite the careful design of an accelerated aging test, the results cannot accurately say that exposure for m hours or m hours will simulate n years of natural aging.
However, since electronic components are not used for several months or even years after they are manufactured, it is very important for equipment manufacturers to maintain their surface wettability, but it must be avoided that the use of a protective layer that will not provide a suitable protective layer in the short term will not be provided. To take an extreme example, an unpassivated silver coating exposed to a sulfiding atmosphere, although initially fully wetted, becomes virtually zero after a few weeks or days (depending on the type and concentration of the sulfide) even with a very strong activated rosin flux. Although it is impossible to accurately predict aging characteristics with a single method, a large body of research has shown that this problem can be adequately addressed by selecting one of the three (in fact, four different) alternative aging test methods listed below as the best aging test method.
8.3.2 Assumed procedures
8.3.2.1 Simulated natural aging should not be outside the range of conditions normally encountered by electronic components, which are temperature 035°C, relative humidity 50% to 95%, and the absence of, for example, sulfur dioxide, hydrogen sulfide, etc. If the specification writer knows that these conditions cannot be met, he cannot and is not allowed to implement the accelerated aging procedure of GB2423.28. If aging is required in this case, a special procedure simulating special nitrogen gas must be used.
8.3.2.2 The specification writer knows that the degradation process of the specified surface can be predicted, intermetallic diffusion or surface changes caused by oxygen or moisture. For the former, the most suitable aging test is Method 3 Dry Heat Test Ba 155℃, 16h) This method can accelerate the diffusion between metals. For the latter, Method 2 (Long-term Wet Heat Test Ca, 10d) is more suitable. 8.3.2.3 If the specification writer cannot predict the change process, or the relevant specification does not give the type of coating, then it is better to use Method 1 (steam aging), and choose 1h or 4h according to the required severity. 1h aging is suitable for the situation where the component is used soon after manufacture, and 4h aging should be selected for samples stored for a long time. 9 Requirements and Statistical Characteristics of Results
9.1 Requirements for Writing Component Specifications
National Standard GB2423.28 specifies the solderability test of electrical and electronic components. This guide describes the basic concepts to help specification writers and users select a particular test method and understand the correct meaning of the results obtained. However, two points of particular importance are not discussed in this document and must be included in the relevant component specifications. These two points are: a. The severity applied; and b. The level of quality assurance achieved by the test. The specification writer must clearly specify these two things, and this accuracy will lead to the statement of various requirements and acceptance limits, the latter of which are based on wettability statistics (see Chapter 6). If these two points are not appropriately specified in the relevant specifications due to ignorance or negligence, the severity and acceptable quality level may not meet the actual needs of the user.
For example:
If the specification writer specifies a wetting time that is too short (e.g. 0.2s) without any real justification, it may cause unnecessary economic losses to the user. If the specified time is too long (e.g. 5s), there will be no difficulty for the component supplier, but the user will have to make a lot of rework. b. If a suitable wetting time is fixed, then the maximum acceptable proportion of defective products must be determined, and sampling must be done with an acceptable confidence level to ensure that this proportion will not be exceeded. It is beyond the scope of this guideline to require this to be done rather than just to draw attention to this problem. The concern of the component specification writer is to carefully select the requirements and limits to ensure that the solderability acceptance level is set at a value that meets the needs of the user. 9.2 Two suggestions for preparing component detailed specifications 9.2.1 In GB2423.28, for each test method a table is given giving the information to be considered in the relevant specification. The specification writer must include this in a clear and correct manner without ambiguity or error. This is more convenient if the relevant specification has a special section for this purpose, although it repeats the information given in other sections and points out that some points are not suitable. 9.2.2 The selection of sampling requirements is statistically related to rejection. Solderability tests are never done alone. It has a statistical nature. Obviously, only a single data is produced for each test method. For example, the solder ball method test in 7.3 gives the wetting time. This can be evaluated using a log-normal distribution diagram. The specific method is as follows: a. Arrange the test results in order from small to large; b. Each reading is given a vertical coordinate distance Y: Y 100m1/2
Where: m—reading sequence number;
Total readings.
Assuming n=50, Y will be an odd number from 1 to 99. Plot the results on logarithmic normal paper,
draw a straight line that fits best;
read the reading B of the straight line at Y=99.99. This gives a probability of one in ten thousand that the welding time is greater than B seconds. Note: This procedure assumes that the 50 data are from the same sample. The smaller the number of samples, the greater the error of the values determined by this method. Therefore, it is recommended that this method should not be used when the number of samples is less than 10. 608
Additional notes:
GB/T 2424.17-1995
This standard was proposed by the Ministry of Electronics Industry of the People's Republic of China. This standard is under the jurisdiction of the Standardization Institute of the Ministry of Electronics Industry. This standard was drafted by the Fifth Institute of the Ministry of Electronics Industry. The main drafter of this standard is Zhang Lezhong.
This standard was first issued in September 1982 and revised for the first time in January 1995. 609
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