Ask the Experts
November 24, 2008 - Updated
November 24, 2008 - Originally Posted

Solder Bump QFN's for Rework

Is it an acceptable practice to "solder bump" pads when replacing a QFN or must you always apply solder paste?


Expert Panel Responses

It is nearly impossible to accurately "solder bump" these components back into place on your PCB. Sure you might have one operator who can achieve satisfactory results, but it will never be reliable enough to meet your quality requirements. For best and repeatable results, you need to remove all residual solder from the site, be sure to clean the site so there are no flux residues. Then print the new solder paste directly onto the pads of the component, ensuring the correct volume for the central grounding pad (too much and the component will float during reflow), pick the component from the paste printing plate with your rework system, align it to the pads on the PCB and place the component. Reflow with the correct thermal profile.

Edward Zamborsky
Regional Sales Manager
OK International Inc.
Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
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