The dwell time, flux and temperatures are main culprits.

Insufficient solder topside fillet occurs where the joint has not formed a good topside fillet. Per IPC acceptability standards, a total maximum of 25% depression, including both the primary solder destination and the secondary solder source sides, is permitted.

When troubleshooting, the primary process setup areas to check include:

• Conveyor speed too slow
• Time over preheat too long, causing the flux to be burned off.
• Dwell time too long, causing flux to be destroyed before exiting the wave.
• Conveyor speed too fast
• Dwell time too short/topside board temp too low.
• Topside board temp too high for flux, causing it to burn off before the wave.
• Insufficient flux, or flux is not active enough.
• Solder temperature too low, and it cools in the barrel before it reaches the topside.
• Wave height too low in one or both waves, so solder does not contact the board properly.

Other things to look for in the process include:

• Solder temperature too high or too low.
• Preheat too high or too low.
• Excess or insufficient flux blow-off.
• Board not seated properly.
• Contaminated flux or solder.
• Board pallet too hot.
• Solder wave height low.
• Flux SP GR too low.
• Conveyor speed high.
• Solder wave uneven.
• Flux SP GR too high.
• Flux applied unevenly or not making contact.

Other things to look for with the assembly:

• Board oxidized, warped or contaminated.
• Mask in hole.
• Laminate moisture.
• Poor plating in the hole.
• Hole and pad misregistration.
• Mask misregistration.
• Component contamination.

Other things to look for with the board design:

• Poor pallet design.
• Internal ground plane.
• Pad size mismatched.
• Large ground plane on component site.
• Lead-to-hole ratio too large or too small.
• Large ground plane on solder side.

Paul Lotosky is global director - customer technical support at Cookson Electronics (cooksonelectronics.com; plotosky@cooksonelectronics.com.

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