SMT Troubleshooting---MT|SMD Problem and Solution?
SMT (Surface Mount Technology), like other SMD Soldering and PCB assembly technology is not ZERO-Defect soldering process. There will always be some or the other defect in any Electronics PCB assembly in both Thru-Hole and SMT.
Here I will discuss some of the most common faults and causes of SMT defects and possible solution and troubleshooting.
Common Faults in SMT:
Solder balls
Solder beading
Bridging
Open- Insufficient
Tombstoning
Unmelted paste
Excessive filet
Slump
Dewetting
Disturb joint
Orange Skinning
Solder Balls – Possible cause:
1.Solder Paste smearing on underside of stencil.
2.What is squeegee pressure?
3.Is stencil underside cleaned with a solvent and is solvent still present after cleaning?
4.Is stencil proper aligned with PCB?
Solution to Solder Ball Problems:
Check squeegee pressure
Check for proper gasketting and alignment
Check if cleaning solvent is completely evaporated before printing
Solution to Oxidised Solder Paste Problems:
Run fresh paste from a different lot under same conditions and see if solder bars go away.
Oxidised paste – Possible cause
Squeegee pressure too high
Paste gets squeezed out between stencil and board
Solution: Reduce squeegee pressure
Possible cause:
Drying out of paste after printing
What is specified tack time of paste?
Possible cause: Paste smearing on underside of stencil
What is squeegee pressure?
Is stencil underside cleaned with a solvent and is solvent still present after cleaning?
Is stencil properly aligned with PCB?
Solution:
Check squeegee pressure
Check for proper gasketting and alignment
Check if cleaning solvent is completely evaporated before printing
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