SMT007 Magazine

SMT007-Apr2024

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84 SMT007 MAGAZINE I APRIL 2024 was first introduced in the C-revision of IPC/WHMA-A-620 Space Addendum § 19.7.2, Mechanical Test Methods—Pull Force (Tensile). For manufacturers of cables or harnesses, the team responsible for the crimping pro- cess should plan to meet pull force test needs according to the frequency and number of sam- ples required. e plan should include the pur- chasing of enough contacts to perform the minimum number of tests. is may require communication between engineering, pro- curement, and manufacturing. is article's comparison of pull test require- ments to technical standards has been con- ducted with respect to the NASA-STD- 8739.4 and IPC/WHMA-A-620 requirements. e requirements were compared with 780 data points retrieved from tensile test logs. All data points met or exceeded the requirements, and no defects were inferred from the records. Despite the study analyzing 780 data points for pull force testing, and all samples passed, this is an insufficient quantity of data points to identify trends on material properties of wires from different suppliers which may have dif- fering metallurgical composition. Additional access to pull testing logs will provide further analysis of crimped termination data to identify additional process control and opportunities to mitigate risk. A sample size of data at least 1 order of magnitude larger will be required to effectively analyze contact/conductor pairs distinguishing between silver/tin plated and nickel-plated wires, and how they vary between suppliers. Machine-readable data from tensile logs, or digital data capture of tensile testing, can significantly ease the burden of sorting and filtering tensile test data, which is commonly hand-written on a paper log. However, defects related to incorrect or mal- formed contacts were observed in the investiga- tion on crimp-related problem failure reports. ese crimp-related incidents were evaluated, and many of the conditions identified were determined to be undetectable by a pull force test (e.g., conductor strands not captured in crimp barrel, damaged insulation, traceability errors, etc.). For this reason, the testing proce- Figure 8: Cross-section of machined contacts.

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