Assessing Manufacturability and Solder Joint Reliability of SMT Connectors
By Heather McCormick and Simin Bagheri, Celestica Inc.

Note: There has been a massive shift of electronic manufacturing from OEMs to the Electronic Manufacturing Services Industry (EMS). As a result, one might wonder what is happening to those R&D, development, and process engineering disciplines necessary for world-class manufacturing. The following Celestica model may not be universal, but this is one EMS company, formerly a subsidiary of IBM, that is doing a lot to both transition and uphold former OEM engineering excellence.
                                                                                                                — John MacWilliams, Bishop & Associates

In recent years, a variety of different connector styles have been introduced to complement or replace traditional pin through-hole (PTH) and press-fit connectors. It is well known throughout the electronics industry that PTH connectors are very reliable when properly mounted to a circuit board. Reliability is one of the most desirable attributes of PTH connectors, but with frequencies increasing, PTH connectors exhibit some limitations in certain applications. Some of these shortcomings include increased inductance from both the connector construction, and connection to the printed wiring board. Other disadvantages include the amount of space required to mount such connectors to the board, the ability to route signals out from the connector to the rest of the board, and the use of the wave soldering process—with its lower yields—to attach them.

As a result of these limitations, alternative connector designs are emerging, such as SMT and area array connectors. Although these styles offer benefits from a signal density and an electrical performance point of view, more emphasis must be placed on solder joint reliability testing, as the surface mount solder joints are not as robust as through-hole attachments. With very limited reliability data available on these alternatives, designers may be hesitant to incorporate SMT connectors into their designs.

Drawing on years of experience in designing test vehicles and conducting solder joint reliability tests for area array and SMT component packages, Celestica is now focusing on connectors’ unique requirements for solder joint reliability testing. While the reliability testing of conventional SMT components, such as ball grid arrays (BGAs), has been standardized in such documents as IPC-9701A and JEDEC JESD22-A104C, similar documents do not exist for connector reliability testing. Connector reliability tests conducted at Celestica over the past five years have aimed to understand the unique issues related to reliability testing of surface mounted and area array connectors, and to develop standards for test vehicle design and reliability test methods for these connectors. Ultimately, this information will be incorporated into IPC-9705, a proposed standard covering the reliability testing requirements for area array and surface mounted connectors.

Working in conjunction with several original equipment manufacturers (OEMs) and connector suppliers, Celestica has designed and built five different connector test vehicles, examining a variety of different area array connector designs, and assessing their reliability in accelerated thermal cycling.

Recently, our work has also focused on lead-free area array connectors. Due to the increased processing temperature required for lead-free assembly, the reflow and rework of area array connectors can be more challenging than for their tin-lead counterparts. Specifically, profiling large thermally massive connectors can be a challenge to the reflow process, and in rework, a proper profile must be achieved while simultaneously preventing damage to the connector body, such as blistering or melting. Celestica has been able to leverage eight years of experience in lead-free process development to help address these issues, and to develop successful manufacturing processes for these connectors. Our current efforts are focused on understanding the reliability of lead-free connectors.

This article was written by Heather McCormick, collaborative development program manager, Celestica, Toronto. McCormick can be reached at hmccormi@celestica.com or 416.446.6331; and Simin Bagheri, project manager, lead-free materials, Celestica, Toronto. Bagheri can be reached at sbagheri@celesica.com or 416.443.7524.

Connector manufacturers and OEMs considering new connector designs can take advantage of Celestica’s experience in test vehicle design and tin-lead and lead-free manufacturing and reliability testing, by working with Celestica’s Engineering Services Team. Test vehicles can be custom designed for reliability and manufacturability assessments of connectors. In addition, test vehicles can be manufactured in Celestica’s prototype facility in Toronto, which is tailored to deal with small manufacturing runs. Mechanical and thermal testing is also available, as well as extensive failure analysis capability.