5 Usual PCB Assembly Defects Detection and Repair

2017-08-02 18:18:00 zhengxiaowei 167

Various welding quality defects happen in the progress of PCB Assembly. It can be caused by a lot reasons, below are 5types common reasons and correspond solutions presented in a form for peer reference.

Defect Type

Picture

Reasons

Solutions

Bridging

Bridging

1.Solder Paste Collapse

2.Reflow Speed too fast

3.Over-dose Solder Paste

4.PCB quality problem, or the PCB back adhesive solder paste

1.Increase the solder paste metal content and viscosity

2.Reduce the squeegee pressure

3.Adjust the temperature curve

4.Using laser cutting template                 

Solder Ball

Solder Ball

1.The solder paste mixed with water

2.Poor solder paste mixed with water

3.Heat speed too fast

4. Components overpressure

1.Enhance the solder paste activity

2.Reduce the temperature

3.Reduce the squeegee pressure

4.Adjust the temperature curve

5.Reduce the components pressure

Tombstoning

Tombstoning

1.Heating too fast and not uniform

2.Components poor weldability  performance

3.The solder paste printing postion offset

1.Adjust the temperature curve

2.Change better weldability performance components

3.Adjust the printing position

Cold Solder

Solder void

1.Stencil in bad quality

2.Solder paste is not enough

3.Scraper too fast

4.The Pad has soldering-resistance layer and dirt

1.Using laser cutting template

2.Increase the stencil openings, reduce the pressure, using metal scraper

3.Decrease the Scraper Speed

4.Check the PCB carefully

Solder Void

Solder void

1.The proportion of the scaling powder in solder paste too large

2.Preheating temperature not high enough

3.Welding time is too short

4.Usually there will have 4% volume contraction when the free-lead solder alloy solidification, it will also cause the solder void if the final solidification area located within the solder joint

1.Adjust the process parameters, Control the preheat temperature and the soldering condition.

2.Ensure the scaling powder proportion in right condition

3.Avoid pollution occurred



TAG:   PCB Assembly Defects