SMTA International Conference Proceedings


Author: Stephen Schoppe
Company: Process Sciences, Inc.
Date Published: 9/25/2005   Conference: SMTA International

Abstract: As lead free assembly processes emerge, the need to rework high I/O (> 1,000) Area Array Packages has become increasingly important. Component & substrate temperature profiles are critical to prevent warpage and promote proper metallurgical bonding. The purpose of this paper is to define general parameters for an optimal hot gas reflow profile to rework high I/O lead free Area Array Packages on organic substrates. Substrate preheat and peak component reflow temperature variables are isolated in different profiles that achieve successful attachment of Area Array Packages.

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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