Easy-to-u advice for common SMT
asmbly issues.
Table of Contents
言出必行Bridging 3Insufficient Fill 7Insufficient Solder 8Random Solder Balls 9Solder Spattering 11Mid-Chip Solder Balls 12Tombstoning 14Voiding 15
BGA Head-on-Pillow 17Grainy Joints 19
With this easy-to-u
Troubleshooting Guide, you can learn to troubleshoot common SMT issues. After using it a few times, it will become an esntial companion for you and anyone in your company responsible for operating an SMT line.
This Guide offers trouble s hoot i ng advice for common SMT asmbly issues by process defect. If your issue is not resolved after follow -ing the steps to help identify the possible root cau and solution,plea contact your Cookson Electronics reprentative who will be able to provide you with further assistance.
Cookson Confidential –For Authorized U Only Alpha SMT
Troubleshooting Guide
星期一到星期日英文
西外Possible Caus: PCB
限制性定语从句
Description
SMD pads will contribute
to coplanarity issue result -
ing in poor gasketing
during printer tup.
西方文学史
Recommendations
Highly recommended
to remove solder mask
between adjacent pads
especially for fine-pitch
components
Possible Caus: Stencil
Description
Dirty stencil with paste
underneath will contam -
inate the bare board on
the next print, attributing
a potential bridge.
Stencil tension
Aperture Design
Recommendations
•Verify zero print gap
t up.
•Ensure minimum print
pressure.
periodic•Increa wipe frequency.
•U different cleaning
汉普森
chemicals.
Ensure stencil tension is
tight. Poor stencil tension
will make it impossible
to have a good tup for
consistent print definition.
For fine pitch component,
it is highly recommended
to have the opening
slightly smaller than
landing pad size to improve
stencil to PCB gasketing. Definition: Solder connecting, in most cas, mis c on -necting two or more adjacent pads that come into contact to form a conductive path.
Bridging
Possible Caus: Screen Printer
Poor gasketing –paste oozes out beneath stencil during printing, increasing chance of wet solder paste bridges
Misaligned print will challenge the paste to pull back to pads during molten stage, increasing the potential for bridging.Smearing and bridging phenomenon on the next printed board after stencil cleaning operation Poor print definition with dog ears especially on fine-pitch components
Dented squeegee blades could result in uneven print pressure.
•Zero print gap between stencil and PCB •Check paste smear underneath stencil. •Check sufficient s
tencil tension.
Ensure print accuracy and consistency for both print strokes.
•Verify stencil is dry after cleaning and before next print.
•Standard cleaning mode is wet/vacuum/dry.•Check board support.•Adjust paration speed to achieve minimum dog ears.
NB: Different paste chem i stry requires different paration speed to minimize dog ears.
Check squeegee blades
condition.
Possible Caus: Component Placement
Placement inaccuracy will narrow the gap between pads, increasing the chance of bridging.Excessive component placement pressure will squeeze paste out of pads.
•Verify component placement pressure.•U X-ray to verify BGA placement.
ground•U microscope for QFPs.•Verify actual component height against data entered in the machine •Component placement height should be ±1/3
of paste height.
Possible Caus: Reflow Profile
harbor
cherylcole
Extended soak will input more heat to the paste and result in paste hot slump phenomenon.
Adopt a straight ramp to spike profile, without soak zone if possible.
