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November 24, 2008

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?



D.W.

Experts Comments

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.

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Edward Zamborsky
Regional Sales Manager
OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
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