tailieunhanh - Conductive Polymers and Plastics in Industrial Applications Part 7

Tham khảo tài liệu 'conductive polymers and plastics in industrial applications part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Microelectronic Encapsulation 123 GLOBTOPS DIE ATTACH ADHESIVES Implicit in the choice of globtops for device protection3 is the fact that if the top of the chip is protected with the globtop the bottom or opposite face of the chip is in contact with some other material. This other material varies with the specific application examples include ceramic substrates printed circuit cards flex substrates and thermal substrates but in many cases the globtop is used because the requirements of interconnection or heat dissipation prevent the use of molded plastic encapsulation. The choice of the globtop is then coupled with the choice of some other material usually a thermally conductive die attach adhesive to bond the other face of the chip to the substrate and reliability of the package is a function of the properties of both these materials and any interaction between the two. In short globtop packaging does increase the options for interconnection and heat dissipation but globtops are not suitable for flipchip attach the mode of interconnection needed for the highest I O chips. Also the chip test burn-in and reworkability features of plastic packages are lost with globtop packaging although some reworkability may be achievable with appropriate materials see below . UNDERFILL FOR FLIPCHIP ATTACH Chip interconnection by use of an array of solder balls bonded to the chip surface significantly increases the number of I Os that can be handled in comparison to peripheral attach via Thermal mismatch between silicon and the substrate in many cases requires that a reinforcing material be applied in the space between the chip and the substrate completely surrounding the solder Like globtop this packaging option makes the opposite face of the chip available for heat dissipation if the array of solder joints do not provide sufficient thermal conductivity to dissipate the heat generated by the device. Depending on the application even if no cap heat .