SMTA International Conference Proceedings

Lead-Free SMT Connector Process Exposure, Reliability, Quality, and Yield Assessment For High Thermal Mass Assemblies

Authors: Jimmy Chow, John McMahon, Heather McCormick, Russell Brush, Vejeyathaas Thambipillai, Kok Wei Khoo, Matt Kelly and Marie Cole
Company: Celestica Inc. and IBM Corporation
Date Published: 10/14/2012   Conference: SMTA International

Abstract: Surface Mount Technology (SMT) connectors are widely used in many server board designs. With the possible expiration of the RoHS "lead in solder" exemption on the horizon, it is critical to optimize manufacturing processes for these connectors on high thermal mass assemblies, to ensure solder joint yields are acceptable without causing thermal damage to plastic connector housings. This challenge has been shown to be even more significant during rework. Solder joint reliability of these connectors must also be assessed. Currently, limited data is available in literature and comparisons to standard BGA devices are not recommended because of the unique structure of these connectors. Accelerated life testing was performed with the intent of predicting their service reliability and discovering dominant failure modes.

A new test vehicle was designed and assembled to study a wide range of connectors for lead-free process assembly and forced rework operations. Solder joint degradation under accelerated thermal cycling was studied for four different connectors. Results are discussed for GIG-Array®, SEARAY™, SlimStack™ connectors and for a Hybrid LGA Socket configuration. In order to in-situ monitor the Hybrid LGA Socket, a daisy-chained LGA Hybrid Interposer was designed and manufactured to simulate an actual LGA. A full mechanical heat sink assembly was mounted around the LGA socket to ensure that cyclic testing was performed under the actual compression stresses that are seen in production level designs. The test vehicle assemblies were preconditioned with shock and vibration prior to accelerated thermal cycling.

Test vehicle design, assembly process parameters, solder joint yield, stress test results, and failure analysis will be presented for this high thermal mass lead-free SMT assembly.

Key Words: 

SMT connectors, lead-free, primary attach, rework, plastic housing survival, solder joint reliability.

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