PCB News - Understand the defects and hazards of PCBA soldering

Understand the defects and hazards of PCBA soldering

The common soldering defects, appearance characteristics, hazards, and cause analysis of PCBA will be explained in detail.

Welding

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.

Hazard: not working properly.

Cause Analysis:

---The component leads are not cleaned, tinned or oxidized.

---The printed board is not clean, and the sprayed flux is of poor quality.

Solder accumulation

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

Hazard: Insufficient mechanical strength, may be welded.

Cause Analysis:

PCB board

---The solder quality is not good.

---The soldering temperature is not enough.

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

Too much solder

Appearance characteristics: The solder surface is convex.

Hazard: Waste solder, and may contain defects.

Cause analysis: the solder withdrawal is too late.

Too little solder

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

Hazard: insufficient mechanical strength.

Cause Analysis:

---The solder fluidity is poor or the solder is withdrawn too early.

---The flux is insufficient.

---The welding time is too short.

rosin welding

Appearance characteristics: Rosin slag is contained in the weld.

Hazard: Insufficient strength, poor continuity, and may be on and off.

Cause Analysis:

---Too many welders or have failed.

---Insufficient welding time and insufficient heating.

---The surface oxide film is not removed.

overheated

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

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

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

cold welding

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

Hazard: low strength, poor electrical conductivity.

Reason analysis: The solder shakes before it solidifies.

poor infiltration

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

Hazard: Low strength, no connection or intermittent connection.

Cause Analysis:

---The weldment is not cleaned up.

---Insufficient flux or poor quality.

---The weldment is not heated sufficiently.

asymmetry

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

Hazard: Insufficient strength.

Cause Analysis:

---The solder has poor fluidity.

---Insufficient flux or poor quality.

---Insufficient heating.

loose

Appearance characteristics: The wire or component lead can be moved.

Hazard: Poor or non-conduction.

Cause Analysis:

---The lead moves before the solder is solidified, causing voids.

---The lead wire is not processed properly (poor or not wetted).

pull the tip

Appearance characteristics: sharp.

Hazard: Poor appearance, easy to cause bridging.

Cause Analysis:

---There is too little flux and the heating time is too long.

---The evacuation angle of the soldering iron is improper.

bridge

Appearance characteristics: adjacent wires are connected.

Hazard: Electrical short circuit.

Cause Analysis:

---Too much solder.

---The evacuation angle of the soldering iron is improper.

pinhole

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

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

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

bubble

Appearance characteristics: There is a spit-fire solder uplift at the root of the lead, and there is a cavity inside.

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

Cause Analysis:

There is a large gap between the lead and the pad hole.

The lead wire is poorly infiltrated.

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

Copper Foil Cocked

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

Hazard: The printed board is damaged.

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

stripping

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

Hazard: Open circuit.

Cause analysis: bad metal plating on the pad.