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This paper describes the challenges of a 17.5um thin bare Cu wire bonding on aluminum bond pads for a fragile low-k wafer technology, on a BGA package. Previous evaluations have so far focused on 20um and 25um bare Cu wires as a suitable low cost replacement for Au wires. To improve performance, more fragile low-k wafer technology is being developed. In the past, some key technical challenges experienced...
A detailed description of the Cu-Al wire bond interface is presented, which can possibly explain the often observed corrosion failures in humidity reliability tests. Using micro-structural analysis techniques, it is shown that the unstressed interface contains up to three intermetallic phases, where the Cu-rich phases are located at the Cu-ball interface. Upon humidity stress test only the high-Cu...
Wire bonding has been the dominant mode of chip to substrate interconnection for many decades. The most common metal used has been gold which is rather malleable and very resistant to oxidation and corrosion. The surge in commodity prices over the last few years has prompted the introduction of copper as a lower cost alternative. While copper has some advantages electrically, thermally and mechanically,...
High gold prices have led to renewed interest in replacing gold with copper in existing packages and new packages in order to save costs. Although reliability is often cited as a reason for using copper, the main driving force for its use is undoubtedly cost. Perceptions that copper wire is more reliable are based on the notion that the intermetallics grow more slowly and that thinner intermetallics...
Electroless nickel and immersion gold (ENIG) is one of the most common final finishes used in PCBs. ENIG surfaces exhibit excellent planarity, solderability and wire bondability and tolerate multiple lead free solder reflows during assembly processing. However, the price of gold has increased rapidly from around $400 US per troy ounce in 2004 to over $1200 US in 2010. This change has increased ENIG...
Advantages of Cu wire bonding, such as less wire sweep, better performance for analog devices, are interpreted by its material properties. Alternative aspect from material properties on Cu wire bonding parameters is proposed to reflect the fact that Cu wire bonding may not necessarily damage the existing under-pad structure of integrated circuit designed for Au wire bonding. The challenge of Cu wire...
The influence of EMC (Epoxy Molding Compound) and reliability with fine Cu wire was studied. It is found that the failure mode was corrosion at the intermetallic layer of the wire bonding part by failure analysis after HAST (Highly Accelerated Temperature & Humidity Stress Test). Al elution and Cl ion was observed at the intermetallic layer. EMC with lower Cl ion content and Al inhibitor of corrosion...
There is growing interest in Cu wire bonding for LSI interconnection due to cost savings and better electrical and mechanical properties. Cu bonding wires, in general, are severely limited in their use compared to Au wires; such as wire oxidation, lower bondability, forming gas of N2+5%H2, and lower reliability. It is difficult for conventional bare Cu wires to achieve the target of LSI application...
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