Metal Finishing Guide Book

2012-2013

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BONDING PROPERTIES (WIRE PULL TESTING) Gold-wire loops (25-��m diameter) (Au HD2) were used to determine any loss in bonding properties after Betatec post-dip treatFigure 8: Crack classification rating 1 to 5, with 1 and 5 showing ment. A pull tester insufficient surface bonding. Ratings 2, 3, and 4 are acceptable. (DAGE 4000) and TSbonder (Delvotek 5410) were used for this study. Wire pull testing determines the quality of the gold wire bond to the surface. It consists of applying a specified upward force under the gold wire attached to the surface. The crack mechanism is studied to evaluate the bond quality. The crack ratings in Figure 8 highlight the Figure 9: Thin gold wire crack rating distribution (as % of population) for Betatec-treated nickel/gold-plated samples. crack at the wire/surface All samples passed the test. interface. Ratings 1 and 5 indicate an insufficient bond with the surface, whereas ratings 2, 3, and 4 are acceptable. Sample processing involved nickel sulphamate (Ni-Sulphamate HS) and pure-bond gold (Aurocor K 24 HF) plating, followed by Betatec post-dip treatFigure 10: Strong discoloration of untreated samples compared to Betatec treatment (above) showing no discoloration after an 8ment. To confirm meahour pressure cooker test. surement reproducibility, 4�� samples were measured and compared to 2�� untreated references. All samples passed the test with no crack ratings of 1 or 5 evident. The majority of samples provided a rating of 3 (central crack), considered the best bonding quality (see Fig. 9). TIN SURFACE PROTECTION STUDY To maximize cost-effectiveness (mentioned in the introduction) many connectors are plated with gold only at the functional contact region with the ���solder flank��� receiving a tin coating. However, the processing sequence does not allow for selective treatment of each region with different post-dips. Hence, the ideal gold post-dip candidate must ensure no detrimental effect on the properties of 280

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