||Due to the concern of human health and the environment issue, Japan and European Union has set a schedule to ban the usage of lead-bear-|
-ed solders. According to the Ministry of Trade and Industry(MITI) regulations, all electronic productions containing lead-beared solders can not
sale in Japan after year of 2002. It has been the trend to use lead-free solders in microelectronics and semiconductor industries. Unfortunately, no lead-free solder that can be fully replace lead-beared solders. So, it is an
urgent issue to study suitable lead-free solders in current electronic Industries.
Some board level’s package, BGA and SMT, have been successfully on the lead-free solder. But some important and key package technologies
, such as C4(Controlled Collapse Chip Connection) and metal heat spreader interconnected with the solder, can not be solved at the moment.
CTE(Coefficient Thermal Expansion) mismatch between Si chip and metal generates the huge thermal stress. So, solder gluing heat spreader
and Si wafer is easily to crack after temperature cycling. Present lead-free solders can not endure the huge thermal stress. So it is important to find a lead-free solder that is compliant and can endure the huge thermal stress.
Having high ductility and well mechanicial property, In-Sn alloys have potential to be used to joint Si chip and metal heat spreader.
To cause the fatigue fracture in solder joint, intermetallic compound plays very important role. If intermetallic compound is too thickness, int-
-erface between the solder and the under bump metallization(UBM) is volunable. Cu is traditional UBM. However, lead-free solders are often Sn--rich alloys, those Sn-rich alloys react easily and rapidly to form Sn-Cu intermetallic compound. After Cu UBM is consumed by soldering reaction, spalling will occur at the interface between the solder and the UBM.Comparing to Cu, Ni reacts slower with Sn-rich alloys. So, here, we select Ni as UBM substrate.
To understand reaction mechanism between In-Sn alloy and bulk-Ni,we designed a experiment to study In-Sn alloy on bulk-Ni, such as wetting angle and intermetallic compound formation. The experimental conditions are: 1.the reflowing time are 10 min＆1 min、2.the reflowing temperature are isothermal 250℃ and 20℃ above melting point of alloys.
There are four differential experiment. We can study the wetting reaction between SnIn/Ni 、SnAgCu/Ni systems. Experimental result will have big contribution on lead-free solder or reactive wetting studies.
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