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A Study of High Cu Behavior on Electrolytic Ni and Electroless Ni Pad Finish
Keywords: High Cu, ENEPIG, Reliability
With increasing use of portable appliances such as PDA and cellular phone, changing environment of application requires higher solder joint reliability. It has been used various pad finish materials to enhance the reliability of solder joint and recently Electroless Ni Electroless Pd Immersion Gold (the following : ENEPIG) pad has been used more than others. This study is about reliability according to being used in commercial Electrolytic Ni pad and ENEPIG pad, and was observed behavior of various Cu contents. After reflow, the inter-metallic compound (IMC) between solder and pad is composed of Cu6Sn5 (Ni substituted) by using EDS, and in case of ENEPIG, between IMC and Ni layer was observed the dark layer (Ni3P layer). Additional, it could be controlled the thickness of dark layer according to Cu contents. Investigated the different fracture mode between electrolytic Ni and ENEPIG pad after drop shock test, in case of soft Ni, accelerated stress propagated along the interface between 1st IMC and 2nd IMC, and in case of ENEPIG pad, accelerated stress propagated along the weaken surface such as dark layer. The unstable interface exists through IMC, pad material and solder bulk by the lattice mismatch, so that the thermal and physical stress due to the continuous exterior impact is transferred to the IMC interface. Therefore, it is strongly requested to control solder morphology, IMC shape and thickness to improve the solder reliability. Moreover, it could be controlled the thickness of 2nd IMC and dark layer according to Cu contents and these behaviors is caused to increase the reliability such as drop strength.
Hyun-Kyu Lee,
DUKSAN HI-METAL CO., LTD.
Ulsan 683-804,
Korea


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