There will be poor welding in PCBA prouction process, due to the influence of various uncontrollable factors such as plate, solder paste, flux, worker, environment and etc. What are the general conditions of poor welding?
1. PCBA board surface residue is too much.
Excessive board residue may be caused by unpreheated or preheated temperature before welding, Tin furnace temperature is not enough; fast board transfer speed; anti-oxidant and anti-oxidation oil added to the tin liquid; too much flux; Components feet and orifices are out of proportion( hole are too large), causing flux build-up; reswulting in flux being used for extended periods of time without the addition of thinner.
2. Corrosion, components turn green, pad becomes black
The corrosion occurred mainly due to the insufficient preheating, which resulted in many flux residues and too many harmful residues; the use of flux that required cleaning, but no cleaning after the completion of welding.
3. Poor welding,continuous welds, missing solder
Poor welding, continuous welds and missing solder are very common problems in welding. The amount of flux applied is too little or uneven, and some of the pads or solder tails are heavily oxidized to cause problems with the solder joints. PCB wiring is unreasonable.; The pins are too dense; Low process level will cause continuous welding; The foam tube is immersed in tin and uneven, which will cause the uneven flux. Also, improper method of operation when hand dipping tin, unreasonable inclination of the chain can also cause problems of continuous welding, and uneven peaks can cause problems of missing welding.
4. Spatter and Tin Bead
The occurrence of spatter and tin bead is generally analyzed from two aspects. The first one is a process problem; the preheating temperature is low ( the flux solent is not completely volatilized); the plate speed is high, and the preheating effect is not reached; the chain inclination bad angle. There is a bubble between the tin liguid and the PCB, and the tin bubble is generated after the air bubble bursts; the hand is not properly handled when immersed in tin; the working environment is wet. The second is the PCB board problem; the board surface is damp, there is moisture; PCB vent hole design is unreasonable, resulting in PCB and tin liquid between the gas; PCB design is unreasonable, the parts are too dense to cause gas.
5. Poor soldering, not full solder joints
Using double peaking process, and the active components of the flux has been completely volatilized in one pass of tin; Slow board transfer speed, and preheating temperature is to high. Nonuniform or too little flux coating doesn not fully wet the pad and components pin. The pad and component pin are heavily oxidized, resulting in poor tinning.
6.PCB solder mask peeling, peeling or blistering.
There may be a problem in the PCB manufacturing process: not cleaning, poor quality solder mask, PCB board and solder mask mismatch. The tin liquid temperature or preheat temperature is too high. the PCB board stays on the surface of the tin liquid for too long; welding too many times.