PCB Technical - Common bad characteristics of PCB circuit board welding

welding circuit board processing manufacturers always have various problems in the process of welding circuit boards. Among them, there are many reasons for poor PCB welding. Here are some common circuit board welding defects, appearance characteristics, hazards, and cause analysis. .

1. PCB virtual soldering

1. Appearance characteristics: There is a clear black boundary between the solder and the lead of the component or with the copper foil, and the solder is recessed toward the boundary.

2. Hazard: not working properly.

3. Reason analysis

1) The leads of PCB components are not cleaned, tinned or oxidized.

2) The printed circuit board is not clean, and the sprayed flux is of poor quality.

2. Solder accumulation

1. Appearance characteristics: The solder joint structure is loose, white and dull.

2. Hazard: Insufficient mechanical strength, possibly false welding.

3. Reason analysis

1) The solder quality is not good.

2) The welding temperature is not enough.

3) When the solder is not solidified, the lead of the component becomes loose.

Three, too much solder

1. Appearance characteristics: the solder surface is convex.

2. Hazard: Waste solder, and may contain defects.

3. Reason analysis: the solder withdrawal is too late.

Four, too little solder

1. Appearance characteristics: The soldering area is less than 80% of the pad, and the solder does not form a smooth transition surface.

2. Hazard: insufficient mechanical strength.

3. Reason analysis

1) The solder fluidity is poor or the solder is withdrawn too early.

2) Insufficient flux.

3) The welding time is too short.

Five, rosin welding

1. Appearance characteristics: Rosin slag is contained in the weld.

2. Hazard: Insufficient strength, poor conduction, and may be on and off at times.

3. Reason analysis

1) Too many welders or have failed.

2) Insufficient welding time and insufficient heating.

3) The surface oxide film is not removed.

Six, overheating

1. Appearance characteristics: white solder joints, no metallic luster, rough surface.

2. Hazard: The pad is easy to peel off and the strength is reduced.

3. Reason analysis: the power of the soldering iron is too large and the heating time is too long.

Seven, cold welding

1. Appearance characteristics: the surface becomes tofu-like particles, and sometimes there may be cracks.

2. Harm: low strength and poor conductivity.

3. Reason analysis: the solder shakes before it solidifies.

8. Poor infiltration

1. Appearance characteristics: The contact between the solder and the welding parts is too large and not smooth.

2. Hazard: low intensity, unavailable or intermittently on and off.

3. Reason analysis

1) The weldment is not cleaned up.

2) Insufficient flux or poor quality.

3) The weldment is not fully heated.

Nine, asymmetry

1. Appearance characteristics: The solder does not flow over the pad.

2. Harm: insufficient strength.

3. Reason analysis

1) The solder has poor fluidity.

2) Insufficient flux or poor quality.

3) Insufficient heating.

Ten, loose

1. Appearance characteristics

The wire or component lead can be moved.

2. Harm

Poor or non-conduction.

3. Reason analysis

1) The lead moves before the solder is solidified and causes a gap.

2) The lead is not well processed (poor or not wetted).

Eleven, sharpen the tip

1. Appearance characteristics: sharp.

2. Harm: Poor appearance can easily cause bridging.

3. Reason analysis

1) Too little flux and too long heating time.

2) Improper evacuation angle of the soldering iron.

12. Bridge

1. Appearance features: adjacent wires are connected.

2. Hazard: electrical short circuit.

3. Reason analysis

1) Too much solder.

2) Improper evacuation angle of the soldering iron.

13. Pinhole

1. Appearance features: visual inspection or low-power amplifier can see holes.

2. Hazard: Insufficient strength, the solder joints are easy to corrode.

3. Reason analysis: the gap between the lead and the pad hole is too large.

14. Bubbles

1. Appearance characteristics: the root of the lead has a flame-breathing solder bulge, and there is a cavity inside.

2. Hazard: Temporary conduction, but it is easy to cause poor conduction for a long time.

3. Reason analysis

1) The gap between the lead and the pad hole is large.

2) Poor lead infiltration.

3) The welding time of the double-sided board plugging the through hole is long, and the air in the hole expands.

15. Copper foil is upturned

1. Appearance characteristics: The copper foil is peeled off from the printed circuit board.

2. Hazard: The welding circuit board has been damaged.

3. Reason analysis: the welding time is too long and the temperature is too high.

16. Stripping

1. Appearance characteristics: the solder joints peel off from the copper foil (not the copper foil and the printed board).

2. Hazard: Open circuit.

3. Reason analysis: bad metal coating on the pad.