QUALIFICATION OF HIGH DENSITY CONNECTOR SOLUTIONS FOR MILITARY AND AVIONIC ENVIRONMENTS Kim Cho, Tim Pearson, David Hillman, Ross Wilcoxon Collins Aerospace Cedar Rapids IA USA [email protected]ABSTRACT This paper discusses the qualification of high density connector solutions for rugged military and avionics environments. As electronic products become progressively smaller in size, there has been a corresponding increase in the demand for miniature, electronic components and the development of high density connectors. The consumer electronics industry has already implemented high density connectors while many avionics/military products still use traditional surface mount and plated through-hole connectors. These traditional connectors are increasingly too large and cannot meet the signal capacity requirements of modern avionics/military product designs within the limited available printed circuit board space. In this study, two major types of high density connectors, the fine-pitch leaded style and the area-array style, were installed on test boards using automated assembly with tin-lead and lead-free soldering processes. The assemblies were subjected to -55°C to +125°C thermal cycle testing in accordance with the IPC- 9701 specification, Performance Tests Methods and Qualification Requirements for Surface Mount Solder Attachments. The first part of this paper discusses the results and observations from the new testing of fine-pitch style (Samtec LSHM) and area-array style (Samtec LPAM/LPAF) connectors. The second part of this paper compares the data for the Samtec LSHM to previously tested area-array connectors (Samtec SEAM/SEAF). Tradeoffs between these two types of connectors, including producibility, reliability, printed circuit board (PCB) space usage, rework, ease of assembly, and defect identification, are discussed. Key words: high density connectors, thermal cycle testing, fine-pitch leaded, area-array BACKGROUND Thermal cycle testing of solder joints is necessary because printed circuit board (PCB) assemblies are made up of many different materials that have different coefficient of thermal expansion (CTE) values. These differences generate mechanical stresses that can crack the weakest link in the assembly. In the case of connectors, the weakest link is typically the solder joint between the connector and the host PCB, due to the CTE mismatch between the plastic housing and the host PCB material. Over the past 20 years, thermal cycle testing of connectors has become increasingly important, due to the replacement of through-hole soldered pins and compliant lead frames with relatively non-compliant solder balls, solder pillars, and fine-pitch “hockey stick” style lead frames. These changes have enabled higher density connectors but have presented challenges in ease of manufacturing assembly and reliability of the solder joint interconnect. Figure 1 shows the progression of connector technology over time. Solder joint reliability is an even larger concern in military and avionics environments. In these harsh environments, the thermal cycling extremes are much greater and occur more frequently than commercial products found in more controlled environments, such as an air conditioned office. Figure 1: Progression of Connector Technology While this paper focuses on solder joint thermal cycle reliability, there are other characteristics that are equally important for the successful application of advanced connector technologies. These parameters include signal speed performance, the robustness of the contact designs and finishes in vibration and shock, and the mitigation of tin whisker risk on matte tin tail finishes, which are not recommended for military and avionics environments. INTRODUCTION Two families of connectors were tested in this experiment. The first was the Samtec LSHM family in vertical and horizontal configurations with input/output (I/O) counts ranging from 40-100. The second was the Samtec LPAM/LPAF family in the vertical configuration with I/O counts ranging from 40-80. The connectors were assembled with tin-lead and lead-free solder and thermal cycle tested in accordance with the IPC-9701 specification. The connectors were subjected to a total of 2000 thermal cycles from -55°C to +125°C with electrical continuity monitored throughout the test. The transition ramp rate was 10C-12C /minute, and all boards were within ±5C of each other during the
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QUALIFICATION OF HIGH DENSITY CONNECTOR ......connectors (Samtec SEAM/SEAF). Tradeoffs between these two types of connectors, including producibility, reliability, printed circuit
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QUALIFICATION OF HIGH DENSITY CONNECTOR SOLUTIONS FOR
MILITARY AND AVIONIC ENVIRONMENTS
Kim Cho, Tim Pearson, David Hillman, Ross Wilcoxon