2022-11-21 21:29

Common problems in PCB terminal welding


PCB terminal blocks, also known as "PCB terminal blocks", are terminal blocks installed on PCB.
Generally speaking, PCB terminal blocks can be divided into four types: plug type, direct welding type, spring type and fence type. For direct welding type, fence type and spring type terminals, their connection to the circuit board mainly depends on the solder pins on the terminal blocks. Plug type terminals are composed of plugs and sockets, and sockets also have solder pins, so the connection to the circuit board also depends on solder pins. In the following, we will introduce the problems that often occur when PCB terminals are welded. I hope it will be helpful to you!
Welding, also known as "welding and fusing", is a kind of manufacturing process and technology to connect metal or other thermoplastic materials by heating, high temperature or high pressure.
Common problems in PCB terminal welding
1、 Faulty soldering
There is a very obvious gray black boundary between the solder and the component lead or between the solder and the copper foil, and the solder is sunken towards the boundary, which causes the terminal to not work normally.
Cause analysis
1) The component leads are not cleaned, tin plated or oxidized;
2) The printed board is not cleaned well, and the quality of the sprayed flux is poor.
2、 Solder buildup
Solder joints are loose, white and lusterless. This may lead to insufficient strength and possible faulty welding!
Cause analysis
1) Poor solder quality;
2) Insufficient welding temperature;
3) When the soldering is not condensed, the component lead is loose.
3、 Too much solder
The solder surface is convex, which not only wastes solder, but also may contain defects.
Cause analysis
Soldering was evacuated too late.
4、 Too little solder
The welding area is less than 80% of the pad, and the solder does not form a smooth joint surface.
Cause analysis
1) Soldering liquidity is poor or solder is withdrawn too early;
2) Insufficient flux;
3) Welding time is too short.
5、 Rosin soldering
The welding seam contains rosin slag, which leads to insufficient strength and poor continuity, and may be on and off.
Cause analysis
1) Too many or invalid welding machines;
2) Insufficient welding time and heating;
3) The surface oxide film is not removed.
6、 Overheating
The solder joint is white, without metallic luster, and the surface is rough. The bonding pad is easy to peel off and the strength is reduced.
Cause analysis
The power of the soldering iron is too high and the heating time is too long.
7、 Cold welding
The surface is like bean curd dregs, sometimes with cracks. It leads to low strength and poor conductivity.
Cause analysis
The solder shakes before condensation.
8、 Poor infiltration
The interface between solder and weldment is too large and not smooth. It leads to low strength, no connection or on/off.
Cause analysis
1) The weldment is not cleaned;
2) Insufficient flux or poor quality;
3) The weldment is not sufficiently heated.
9、 Asymmetry
Solder does not flow full of pads, resulting in insufficient strength.
Cause analysis
1) Poor fluidity of solder;
2) Insufficient flux or poor quality;
3) Insufficient heating.
10、 Loosening
Wires or component leads can move, resulting in poor or no continuity.
Cause analysis
1) The lead wire moves to cause the gap before the soldering is not condensed;
2) The lead wire is not well treated (poor or not soaked).
11、 Gib
The appearance is poor due to sharp, which is easy to cause bridging.
Cause analysis
1) Too little flux and too long heating time;
2) The withdrawal angle of soldering iron is improper.
12、 Bridging
Adjacent wires are connected, causing electrical short circuit.
Cause analysis
1) Excessive soldering;
2) The withdrawal angle of soldering iron is improper.
13、 Pinhole
Visual inspection or low-power amplifier can see holes. As a result, the strength is insufficient and the solder joint is easy to corrode.
Cause analysis
The clearance between the lead wire and the pad hole is too large.
14、 Bubble
The root of the lead has a flame spraying solder bulge, and there are cavities inside. Although the conduction is temporary, it is easy to cause poor conduction for a long time.
Cause analysis
1) Large clearance between lead wire and pad hole;
2) Poor infiltration of lead wire;
3) The welding time of double-sided plate plug through-hole is long, and the air in the hole expands.
15、 Copper foil cocks up
The copper foil is stripped from the printed board, causing the printed board to be damaged.
Cause analysis
The welding time is too long and the temperature is too high.
16、 Stripping
The solder joint peels off from the copper foil (not from the copper foil and printed circuit board), resulting in an open circuit.
Cause analysis
Poor metal coating on the pad.

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