Abstract
Electroless Ni(P)/electroless Pd/immersion Au (ENEPIG) is a common surface finish in electronic packaging, while the Ni(P) layer increases the impedance of solder joints and leads to signal quality degradation in high-frequency circuits. Reducing the thickness of the Ni(P) layer can balance the high impedance and weldability. In this paper, the interfacial reaction process between ultrathin ENEPIG substrates with different Ni layer thicknesses (0.112 and 0.185 μm) and Sn–3.0Ag–0.5Cu (SAC305) solder during reflow and aging was studied. The bonding ability and reliability of solder joints with different surface finishes were evaluated based on solder ball shear test, drop test and temperature cycle test (TCT), and the failure mechanism was analyzed from the perspective of intermetallic compound (IMC) interface growth. The results showed that the Ni–Sn–P layer generated by ultrathin ENEPIG can inhibit the growth of brittle IMC so that the solder joints maintain high shear strength. Ultrathin ENEPIG with a Ni layer thickness of 0.185 μm had no failure cracks under thermal cycling and drop impact, which can meet actual reliability standards. Therefore, ultrathin ENEPIG has broad prospects and important significance in the field of high-frequency chip substrate design and manufacturing.
Highlights
With the development of the electronic information industry, electronic packaging technology is focusing on the direction of high function, high density and high integration [1,2]
The results showed that there was no significant difference between the two surface finishes in low-speed shear tests, but because the intermetallic compound (IMC) layer of thin ENEPIG was thicker than that of normal ENEPIG, the adhesion of thin ENEPIG was poor in high-speed shear
This paper focuses on the changes in IMC composition during the interface reaction of the ultrathin Ni(P) layer ENEPIG, which has previously been studied less
Summary
With the development of the electronic information industry, electronic packaging technology is focusing on the direction of high function, high density and high integration [1,2]. Solder joint reliability is an important research content of modern electronic packaging technology [3,4,5]. The surface finish of printed circuit boards (PCBs) has attracted more and more attention because of its protective effect on exposed copper circuits and for providing a good soldering surface, which affects the reliability of electronic packaging solder joints [6,7,8]. Tin (ImSn), Nickel–Gold (NiAu) and Electroless Nickel/Immersion Gold (ENIG), ENEPIG has the advantages of good thermal stability, high weldability, low cost and no black pad phenomenon, like ENIG [9,10,11,12,13], and can be applied to a variety of packaging forms.
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