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November 10, 2008 - Updated November 10, 2008 - Originally Posted Opens on BGA Solder JointsWe are seeing some unknown solid substances around PCB pads after reflow soldering. These substances appear to be causeing opens on some BGA solder joints. How can we identify the composition of these substances? How can we confirm what has caused this problem? E. W. |
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Expert Panel Responses | |||||||
The answer to the question is the development of an analytical test protocol.
VP Engineering Services STI Electronics Inc. Mark T. McMeen is STI Electronics Inc.ʼs Vice President of Engineering Services. He oversees the daily operations of the Engineering Services division of STI. He has over 18 years experience in the manufacturing and engineering of PCBs.
Contaminants on the BGA balls (left behind on the balls due to due to improper cleaning during the BGA mfg process) may be interfering with the solder paste during the SMT process; and causing the opens. There have been instances where plain tap water has been used to clean the BGA instead of DI water - during SMT reflow, these contaminants reacted with solder paste to form solid "gunk" and caused opens. BGA ball cleanliness needs to be verified. Also a BGA mfg process that uses a no-clean process could result in a wider process window because no contaminants are introduced due to a cleaning step. SEM-EDS & Raman Spectroscopy can be used to analyze the composition. Technical Manager - Europe Indium Corp. Currently with Indium Corporation and responsible for technology programs and technical support for customers in Europe. Over 15 yrs experience in SMT, Power, Thermal & Semiconductor Applications. Masters Degree in Industrial Engg, State University of New York-Binghamton.
From what you describe, it sounds like flux residues that are being left on the pcb. This can occur from either; too high a reflow temperature causing the flux to burn and contaminate the pcb or too low a reflow temperature causing the flux to wet to the board but not allow the solder balls to melt. You first order of finding a solution would be to use an optical inspection system like the VPI-1000 from Easy Braid Corp., It will allow you to look under mounted BGAs and determine what the material is. 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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