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ENEPIG0.08 0.08 0.06 0.06
ENEPIG0.05 0.05 0.08 0.14
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Fig. 1.
Schematics of solder ball attachment on (a) conventional ENEPIG and (b) ultrathin-ENEPIG metallization.
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Fig. 2.
Electrical resistance of solder joints for ENEPIG and selected ultrathin-ENEPIG before and after reflow process.
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3. Results and discussion
3.1. Microstructural calpain inhibitor 1 of interfacial reaction product
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Fig. 3.
Cross-sectional BSE micrographs of interfacial region of SAC305 jointed with (a) commercial ENEPIG, (b) ENEPIG0.31, (c) ENEPIG0.26, (d) ENEPIG0.18, (e) ENEPIG0.08, (f) ENEPIG0.05.
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Fig. 4 zooms the interfacial region of SAC305/ENEPIG0.31 and ENEPIG0.18. It appears that P-rich layer in Fig. 4(a) is thicker than those in Fig. 4(b) and (c) because of the thick Ni(P) deposit and more P content in metallization layer. P-rich layer was not formed when the Ni(P) thickness was less than 0.08 μm because the P concentration in solder joints was too little for solder reaction-assisted crystallization. The composition of each P-rich layer was investigated by FE-EPMA quantitative analysis and listed in Table 2. Phase of the layer-type IMC far from the patch-like (Cu,Ni)6Sn5 (point A) in Fig. 4(a) and layer with dark contrast (point C) in Fig. 4(b) were identified as Ni3P. In contrary, phase of the layer-type IMC near the (Cu,Ni)6Sn5 patch (point B) in Fig. 4(a) and IMC layer in Fig. 4(c) with bright contrast (point D) was Ni2Sn1+xP1−x.