Pan Pacific Symposium Conference Proceedings


Authors: Heather McCormick, et al.
Company: Celestica Inc., Alcatel-Lucent, and FCI
Date Published: 2/12/2009   Conference: Pan Pacific Symposium

Abstract: Area array connectors have become popular in a variety of electronic products due to the benefits they can provide in routing density and signal integrity, and their potential to simplify manufacturing processes by eliminating the need for wave soldering. While the amount of data available on the reliability of these connectors continues to grow, the transition of many products to lead free has required new, lead free versions of area array connectors to be developed. The “Metro2” test vehicle aimed to assess the reliability of some of these new, lead free area array connectors. This paper summarizes the findings in three key areas: the reliability of lead free area array connectors as compared with tin/lead area array connectors, the effect of test vehicle design variables on the reliability of the lead free connectors, and finally, the impact of repeated mating and unmating on the performance of the connectors in accelerated thermal cycling.

Two different lead free mezzanine connectors, and two versions of lead free area array backplane connectors were included on the “Metro2” test vehicle, 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” test vehicle, which used tin/lead versions of these same connectors.

Results from the original “Metro” test vehicle suggested that design parameters may impact the reliability and/or failure mode of mezzanine connectors. The “Metro2” test vehicle was designed to assess the impact of changing the total stack height of the connector from 4 mm to 6 mm, and also the impact of changing the thickness of the daughtercard from 0.062” to 0.093”. The thermal cycling results and failure modes are discussed. This data will assist in developing recommendations for area array test vehicle designs in an effort to standardize the reliability testing of area array mezzanine connectors.

In some cases, such as high I/O connectors and multiple connectors, the mating and un-mating forces on connectors can be substantial. A sub-set of test vehicles were subjected to twenty five mating and unmating cycles on the daughtercard, and fifty mating and unmating cycles on the backplane prior to being added to the chamber for thermal cycling to determine if the reliability of the connectors was degraded by the forces experienced by the solder joints in the mating and unmating processes.

Key words: Area Array Connectors, Lead Free Assembly, Reliability

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