Causes and Countermeasures of "welding knowledge" wave soldering

Date：2022-06-13 15:42:36Views：1082

What is the cause of faulty soldering in wave soldering? The appearance of wave soldering is characterized by rough granular surface, poor gloss and poor fluidity. In essence, any copper tin alloy layer with appropriate thickness is not formed on the brazed connection interface, which is called false soldering. To help you have a better understanding, the following contents are sorted out by Chuangxin testing network for your reference.

What is wave soldering?

Wave soldering is one of the main causes of upper part defects in dip process. The defect rate caused by wave soldering in the whole PCBA assembly process is as high as 50%. However, in terms of appearance, the surface of the solder joint is rough and granular, with poor gloss and poor fluidity. The essence is that no alloy layer (IMC) of appropriate thickness is formed on the interface of the joint during the welding process. At this time, if the solder joint is uncovered, it can be found that there is no residue wedged between the base metal and the solder. The interface is flat and clear, just like gluing together.

Causes of faulty wave soldering:

1. PCB warps, resulting in poor contact between PCB tilt position and wave crest welding.

2. PCB design is unreasonable, and the shadow effect caused by wave soldering leads to missing soldering.

3. the use of single-layer electrode at welding temperature causes poor adhesion or capping of chip metal electrode head.

4. component pads, leads and PCB substrates are oxidized or contaminated, or PCB is wet.

5. both sides of the conveyor belt are not parallel, so the PCB and Apollo peak contacts are not parallel.

6. poor wettability due to poor flux activity. The preheating temperature of high-voltage circuit breaker is too high, which leads to the carbonization of flux, loss of activity and poor wettability.

7. the peak is not flat, and the height of both sides of the peak is not parallel. In particular, if the tin wave nozzle of the electromagnetic pump wave welding feeder is blocked by oxide, the wave crest will be tortuous, which is easy to cause missing welding and cold welding.

Improvement measures for faulty soldering of circuit board after wave soldering:

1. Components and parts shall be used first come, first served. They shall not be stored in a humid environment. They shall not exceed the specified use date. PCB shall be cleaned and dehumidified;

2. Surface mounted components with three-layer end structure shall be selected for wave soldering, and the component body and welding end can withstand more than two 260 ° wave soldering temperature shocks;

3. The layout and arrangement direction of components and parts shall follow the principle of small components in front and avoiding mutual shielding as far as possible, and the length of the remaining pad after the components are overlapped can be appropriately lengthened;

4. The warpage of PCB is less than 0.8 to 1%;

5. Adjust the horizontal level of wave soldering machine and transmission belt or PCB transmission frame;

6. Clean the wave crest nozzle;

7. Replace the flux;

8. Set the proper preheating temperature.

The above are the causes of the wave soldering and the improvement measures related to the core detection and sorting. I hope it will be helpful to you. Shenzhen Chuangxin Online Testing Technology Co., Ltd. is a well-known professional testing institution for electronic components in China, with 3 standardized laboratories covering an area of more than 1000 square meters. The scope of testing services covers: testing and verification of electronic components, IC authenticity identification, material selection for product design, failure analysis, function testing, factory incoming material inspection, X-ray testing of components and parts, tape braiding and other testing items.