THE OPTIMIZED REFLOW PROFILE FOR REWORK OF HIGH I/O LEAD FREE AREA ARRAY PACKAGESAuthor: Stephen Schoppe
Company: Process Sciences, Inc.
Date Published: 9/25/2005 Conference: SMTA International
Determination of a successful attachment is initially done using transmissive X-Ray techniques. Uniformity of solder sphere size, as well as the presence and size of solder voiding are the criteria used for 1st level inspections. A second level investigation was done by evaluating the repeatability of each reflow profile. A set of 16 assemblies was processed for each reflow profile. A profile that generated two failing attachments as determined by X-Ray analysis was then disqualified. Final criteria for selection of the optimized profile was done using metallurgical crosssectioning techniques.
Criteria for cross-section inspections include the quantification of solder ball compression to access the amount of component and/or substrate warpage. The sections were etched to allow for accurate thickness measurement of the intermetallic layer using a Scanning Electron Microscope. Other inspection criteria used for evaluated included the size/ location of solder voiding and grain structure of the solder joint.
Key words: BGA, rework, warpage, lead-free
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