PCB Blog - What are the reasons why PCB board pads are not easy to tin

How to deal with soldering tin on PCB board, first of all, the internal hot soldering iron is introduced. For the current PCB process, the soldering head of the hot soldering iron is relatively large and thick, but the PCB components at that time were discrete and large, so it can be used. Later, the method of throwing tin was often used. The specific operations were as follows: Dip the iron head in the rosin box, and then shake the iron quickly. The solder on the iron head will be thrown into the rosin. After that, use the soldering iron head to solder the original pin that needs to be removed. Repeat several times to suck the original solder away.

Again, the tin suction device will be on the stage. It is like a syringe, which uses the adsorption force to suck the melted solder into the cavity. Use a soldering iron to heat the soldering tin to the melting state, and then use a tin suction device to quickly remove it. Then someone invented the tin absorbing tape, which is a copper wire mesh similar to the shield wire. Pure copper is particularly easy to eat tin. It is hollow inside and has a lot of space. Large and clean tin absorption capacity! When using, put the tin absorbing strip on the bonding pad, heat the soldering iron directly on the tin absorbing strip, and the solder will be absorbed by the tin absorbing strip immediately after melting. If not, it can also be replaced by multi strand soft copper wire. A smaller circuit board can also use jitter to remove tin. After the solder pad is heated, gently shake it on the table, and the melted solder will flow down. Large area tin removal can be heated as a whole, and the solder will flow down after melting. The purpose of fast tin removal and original removal is achieved. It should be noted that the smoke from soldering tin and rosin is toxic, so pay attention to ventilation during use.

As we all know, it is not easy to tin the PCB board pad, which will affect the component mounting, thus indirectly leading to the failure of subsequent tests. What are the reasons why PCB pads are not easy to tin? I hope you can avoid these problems when making and using, and minimize the loss.

The first reason is that we need to consider whether it is a problem designed by the customer. We need to check whether there is a connection mode between the pad and the copper sheet that will lead to insufficient heating of the pad.

The second reason is whether there are problems in customer operation. If the welding method is not correct, it will affect the insufficient heating power, temperature and contact time.

The third reason is: improper storage.

1) Normally, the tin spraying surface will be completely oxidized or even shorter in about a week;

2) OSP surface treatment process can be kept for about 3 months;

3) The gold plate shall be kept for a long time.

The fourth reason is the problem of flux.

1) Inadequate activity and failure to completely remove the oxidation substances of PCB pad or SMD welding position;

2) The amount of solder paste at the solder joint is not enough, and the wettability of the flux in the solder paste is poor;

3) The tin on some solder joints is not full, and the flux and tin powder may not be fully mixed before use;

The fifth reason is: the problem handled by the board factory. There are oily substances on the pad that have not been removed, and the pad surface has not been oxidized before leaving the factory.

The sixth reason is: reflow problem. Too long preheating time or too high preheating temperature will lead to failure of flux activity; The temperature is too low or the speed is too fast, and the tin on the PCB board does not melt.