An Investigation of Lead Free and Bromine Free Technologies for Medium Power Semiconductor Packaging
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An Investigation of Lead Free and Bromine Free Technologies for Medium Power Semiconductor Packaging Philip Adamson and Pamela Dugdale Assembly Research and Development, International Rectifier GB, Hurst Green, Surrey, RH8 9BB, U.K.
ABSTRACT Over recent years there has been a growing interest in the removal or substitution of Lead, Bromine and other hazardous chemicals from electronic and electrical equipment. This relates primarily to products whose end of life disposal relies on the use of landfill sites or increasingly on recycling. The driving force for these changes come from both legislation such as that proposed by the European Union [1] and also from consumer awareness. The implications of the move towards more environmentally friendly electronics extend right down the level of discrete component packages including those produced in large numbers by the power semiconductor industry. In the present paper the technical challenges associated with the development of a lead and bromine free medium power packaging are discussed and the results of ongoing investigations are presented. The major challenges in this area relate not only to the substitution of key elements but also to ensuring compatibility with the higher reflow temperatures which may be associated with Pb-free surface mount processing. This raises particular issues with respect to the die attach material, which is often a high Pb soft solder; the encapsulation compounds which tend to rely on Bromine and Antimony compounds for their flame retardant properties; and the device plating which must be compatible with Pb-free board attach solders.
INTRODUCTION The implications of the move to lead free electronics are being widely studied [2,3]. Much of the work focuses on determining the best alternative to eutectic tin lead solders for surface mounting passive and active devices. Studies are underway for both wave and reflow soldering, most of which indicate the use of SnAgCu alloys with melting points around 217oC and reflow temperature of around 260oC. Less work has been done to ensure that lead and bromine free electronic and semiconductor components will be compatible with the new surface mounting technologies and reliable. This provides us with a highly technical challenge. . Before considering in more detail the ‘lead-free’ package the current status of the chemical content of a typical power semiconductor device is presented. Table 1 gives a breakdown for a TO220 MOSFET.
N5.4.1
Table 1. Chemical content of a typical TO220 power HEXFET ™ No.
Name of the Part
1
Heatsink
2
Die (Typical)
3
Die Solder
4 5
Wire Lead and Heatsink Solder plate
6
Case Mould
TO220 TABLE OF MATERIAL DECLARATION Material Material Materials Mass Name Analysis (Gram) (Element) .65 Plated Cu Cu .005 Ni .007 Semiconductor Si .000042 .000005 .0000017 .0000017 .0052 .0019 .00048 .0065 .0002 .0018 .445 .127
Al Cr Ni Ag Sn Ag Sb
Alloy
Al Alloy
Pb Sn Silica Epoxy Resin Sb Oxide + Br
Plastic
.01
Material Analysis (Weight %) 99.2 0.79 98.785 0.64 0.075 0.25 0.25 65
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