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Thursday, 26 March 2009 17:18

Connectors

“Area Array Connectors: Transition to Lead-Free”

Authors: Heather McCormick, Alex Chan, Richard Coyle and Donald Harper; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: The Metro2 test vehicle aimed to assess the reliability of some new, Pb-free area array connectors. This paper summarizes findings in three key areas: the reliability of Pb-free area array connectors as compared with SnPb area array connectors, the effect of TV design variables on the reliability of the Pb-free connectors, and finally, the impact of repeated mating and unmating on the performance of the connectors in accelerated thermal cycling. Two different Pb-free mezzanine connectors and two versions of Pb-free area array backplane connectors were included on the Metro2 TV, which was subjected to 6000 cycles of accelerated thermal cycling from 0°C to 100°C in accordance with IPC-9701A. The results for the two mezzanine connectors are compared with the results from the original Metro TV, which used SnPb versions of these same connectors. Results from the original Metro TV suggested that design parameters may impact the reliability and/or failure mode of mezzanine connectors. The Metro2 TV was designed to assess the impact of changing the total stack height of the connector from 4 to 6 mm, and also the impact of changing the thickness of the daughtercard from 0.062" to 0.093". Thermal cycling results and failure modes are discussed. In some cases, such as high I/O connectors and multiple connectors, the mating and unmating forces on connectors can be substantial. A subset of TVs were subject to 25 mating and unmating cycles on the daughtercard, and 50 mating and unmating cycles on the backplane prior to being added to the chamber for thermal cycling to determine if the connector reliability was degraded by the forces experienced by the solder joints -in- the mating and unmating processes. (SMTA Pan Pac Microelectronics Symposium, February 2009)

Soldering

“Resolution of Solder Voids in Pin Hole Product”

Authors: Condia Yu, Phil Isaacs, et al; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: What happens when a defect appears that is new, unique and so different from the typical defect that it is not readily apparent what caused it, or whether it occurred during PWB manufacturing, assembly or, through an interaction between the two processes? A unique plated through-hole solder void that did not meet IPC Class II PCB workmanship requirements per IPC-A-610 occurred on a large number of assemblies. Several questions immediately arose: What caused the defect? Is the product acceptable for customer shipment? Can the defective product be reworked? Is this a seasonal defect (e.g., laminate voids caused by high levels of moisture in the laminate) or has a process variable shifted? A team of engineers from multiple companies worked together to answer these questions. (SMTA Pan Pac Microelectronics Symposium, February 2009)

Testing

“Strain Gage Testing: The Delta Effect of Thermal Cycle Testing"

Author: Mark T. McMeen; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: This article looks at one case study of failed hardware and the underlying failure mechanisms of temperature cycling. Strain gage testing has been used on specific applications to understand the applied strain and strain rates applied to PCB assemblies from environmental forces during their working life. Use of Pb-free alloys opens these finished assemblies to fracturing due to CTE (coefficient of thermal expansion) fatigue and strain forces. This review looks at the effect of CTE movement and strain imparted from burn-in or accelerated life-cycling to determine the weak link in the overall design of the system. The use of the mathematical formula Y-X or X-Y to determine the peak-to-peak amplitude and its corresponding delta difference from tension-to-compression or vice-versa is the essential information needed to determine impact over time. Also essential is the dwell or duration of stress over time, which can be the silent killer in some applications because it is temperature/time profile analysis overlaid with the strain gage data to capture time and temperature effects of CTE movement and strain levels on certain component locations. (SMTA Pan Pac Microelectronics Symposium, February 2009)

“Prognostics-Based Product Qualification”

Authors: Michael Pecht and Jie Gu; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: Qualification is the process of demonstrating that a product is capable of meeting or exceeding specified requirements. The specified requirements are expected to depend on the final product and its specific lifecycle application conditions. In most cases, the traditional qualification process has not been efficient or cost-effective. This paper proposes a prognostics-based qualification. The approach does not require a product to fail in the test, because in addition to detecting failure, the health of the product is monitored, including degraded health and intermittent product disruptions. The results are a significant decrease in qualification time and much-improved understanding of product reliability. (SMTA Pan Pac Microelectronics Symposium, February 2009)

Last Updated on Wednesday, 01 April 2009 11:50
 

Columns

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For the first time in years we see parity in the Eastern US among EMS factories from Asia, Mexico and the US. This EMS market condition will permit American OEMs (the EMS industry refers to OEMs as customers) to have more EMS pathways to choose from. Now more than ever, such EMS assignments will require deeper investigation relating to the OEMs’ evaluation of manufacturing strategies.

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