Ask the Experts
August 30, 2010 - Updated
August 29, 2010 - Originally Posted

SMT Components Popping Off During Reflow

One particular SMT component is popping off during the reflow process leaving indentations in the solder. Could the fans in our convection reflow system be blowing this part off the PCB or is it more likely due to a component moisture problem?

D. L.

Expert Panel Responses

This is more likely a consequence of out gassing. The components, the PCB, or the paste may be moisture heavy and will need to be treated in an appropriate fashion to remove the moisture content. Either dried in an oven [see Moisture Sensitivity articles for drying conditions.] or in the case of the paste conditioned and treated per the suppliers recommended methods. In some cases such a phenomena will occur over blind via's and again is moisture or trapped gas in the via expanding explosively dislodging the parts over or close to the via. Lastly I would check the cure on the solder resist, if it is not completely cured it too will continue to out-gas and create problems.

Allen W. Duck
ATEK llc
Allen Duck is a 20-year Electronics Industry veteran with Global experience in multiple fields of technology and management. He started A-Tek in 2006 to provide a sales and service channel for international equipment companies wishing to offer value based solutions to USA companies.

Can you see any bulging or deformation along the bottom face (underside) of the components that popped off? If so that's a tell tale sign that you had a moisture problem. If unsure you may want to experiment by baking a batch of the component PN in question prior to use. For the experiment be sure to use new components that were not previously exposed to reflow temperatures. Bake them before use according to Table 4-1 of IPC/JEDEC J-STD-033B. If baking makes the problem go away, then you likely had a moisture problem and an audit of your MSD floor life tracking procedure is recommended. More information on this topic is available from Cogiscan's online Knowledge Center:

Mitch DeCaire
Sales Manager (Americas)
Cogiscan, Inc.
Mitch DeCaire, Sales Manager at Cogiscan, has served the electronics manufacturing industry since 1989. His prior experiences include process engineering, business development, and engineering management roles with Nortel Networks, Vansco Electronics, Universal Instruments and Siemens.

If there are indentations in the remaining solder, it sounds like the component has a solderability problem that is causing the component not to wet. This solderability issue could be made worse by the cooling fans dislodging the unsoldered component. So start with the problem part and then work backwards to see why it's not wetting. It could be storage issues, contamination of the plated areas or lead / lead free solder mismatch.

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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