Analysis of bad welding quality and countermeasures

1.Common parameters

( 1 ) Peak height refers to the peak soldering PCB's tin height. Its value is usually controlled by 1 / 2 ~ 2 / 3 of the thickness of the PCB.When it exceeds this range,it will cause the molten solder to flow to the surface of the PCB, forming the bridge connection and the damage of the PCB.

( 2 ) The wave soldering machine should also adjust the inclination of the transmission device when it is installed, in addition to the level of the machine, the adjustment of the dip angle can control the welding time of PCB and the wave crest surface, and the proper dip angle helps the solder liquid to be separated from the PCB more quickly, so that it can return to the tin bath.

( 3 ) the effect of solder purity on welding. In the wave soldering process, the impurities in the solder are mainly copper and oxide on the PCB pad and the component pins, an excessive amount of copper leads to an increase in welding defects.

( 4 ) Adjusting the process parameters of wave soldering machine process parameters : belt speed, preheating time, welding time and inclination need to be coordinated with each other.

2.Analysis of bad welding quality and countermeasures:

( 1 ) Pull the tip.

The reasons are as follows :

a. There are glitches on the component pins;

b.The soldering temperature of tin stove is too low;

c. Preheating temperature is too high or time is too long;

d. The soldering time is too long; flux density is too low, spray is not normal.

( 2 )There are pores on the solder joint.

The reason analysis is :  the component pin is polluted; short circuit plug, fixture damage, pin too long, tin temperature is too low, solder time is too long, flux selection is wrong, welding spray is not normal, the solder wave is not normal, and the phenomenon of interference flow, the welding angle is too small.

( 3 ) Resistance to Welding. Cause analysis : part pollution, PCB oxidation, solder liquid impurities too much, solder time is too short.

( 4 ) Excessive solder.

Reason analysis : fixture damage, second tin, solder resist printing is not enough, tin liquid impurities is to much.

( 5 )Cold welding

Reason analysis : the conveyor belt vibration phenomenon, the speed is too fast, wave soldering height is not enough, the solder wave surface is not normal, the fixture overheating.

( 6 ) Air welding.

Reason analysis : printed circuit board oxidation, contaminated, flux spray is not normal, the solder wave is not normal, there is turbulence phenomenon, the preheating temperature is too high, the soldering time is too short.

( 7 ) Solder ball phenomenon.

Cause analysis : flux spray is not normal, tin liquid impurities are excessive, peak tin surface is not stable, printed circuit boards and parts are contaminated, the preheating temperature is too high, too low, the soldering time is too short, and the track of the welding process has chattering phenomenon.

This article is from Allicdata Electronics Limited.