WE CONTINUE OUR series on solder bridging. This month, we look at potential problems caused by the placement machine and reflow profile.
If the pick-and-place machine is suspected:
Problem: Placement inaccuracy narrows gap between pads, increasing the chance of bridging.
* Verify component placement pressure.
* Use x-ray to verify BGA placement.
* Use microscope for QFPs.
Problem: Excessive component placement pressure will squeeze paste out of pads. Recommendations:
* Verify actual component height against data entered in the machine.
* Component placement height should be [+ or -]1/3 of paste height.
If the reflow profile is suspected:
Problem: Extended soak will input more heat to the paste and result in paste hot slump phenomenon.