Analysis of welding quality what are the causes of reflow defects?

Date：2022-05-25 14:52:51Views：864

SMT reflow soldering is a very important SMT process. It is a welding process in which the chip components are combined with the pad on the circuit board through high temperature and then cooled together, which has a great impact on the service stability of the circuit board. Some process defects are also easy to appear in reflow welding. It is necessary to analyze the causes and solve them to ensure product quality. In order to help you have an in-depth understanding, this paper will summarize the relevant knowledge of reflow defect analysis. If you are interested in what this article will cover, read on.

Solder balls:

1. The silk screen hole is not aligned with the pad, and the printing is inaccurate, which makes the solder paste dirty the PCB.

2. The solder paste is exposed too much in the oxidizing environment and absorbs too much water in the air.

3. Heating is inaccurate, too slow and uneven.

4. The heating rate is too fast and the preheating interval is too long.

5. The solder paste dries too fast.

6. Insufficient flux activity.

7. Too many small particles of tin powder.

8. Improper volatility of flux during reflow.

The process approval standard of solder balls is that when the distance between pads or printed wires is 0.13MM, the diameter of solder beads shall not exceed 0.13MM, or more than five solder beads shall not appear within 600mm2.

Bridging: Generally speaking, the factors causing the tin bridge are that the solder paste is too thin. SMT patch processing includes low metal or solid content in the solder paste, low shake solubility, easy pressing of the solder paste, too large solder paste particles and too small surface tension of flux. There is too much solder paste on the pad and the peak reflow temperature is too high.

Open:

1. Insufficient amount of solder paste.

2. The coplanarity of component pins is not enough.

3. Tin is not wet enough (insufficient melting and poor fluidity), and the solder paste is too thin, resulting in tin loss.

4. The pin absorbs tin (like corduroy) or there is a connecting hole nearby. The coplanarity of pins is particularly important for pin components with dense spacing and ultra-dense spacing. One solution is to tin the pad in advance. Tin absorption of pins can be prevented by slowing down the heating speed, heating more on the bottom and less on the top. A flux with slow wetting speed and high activity temperature can also be used, or a solder paste with different Sn / Pb ratio to block melting can be used to reduce the tin absorption of the pin.

The above is the related content of reflow defect analysis of core detection and small editing. I hope it will be helpful to you. Shenzhen Chuangxin Online Testing Technology Co., Ltd. is a well-known professional testing organization for electronic components in China. It has three standardized laboratories with an area of more than 1000 square meters. The scope of testing services covers: testing and verification of electronic components, identification of IC authenticity, product design, material selection, failure analysis, function testing, factory incoming material inspection, X-ray testing of components, tape braiding and other testing items.