Studies on various chip-on-film (COF) packages using ultra fine pitch two-metal layer flexible printed circuits (two-metal layer FPCs)

0026-2714/$ see front matter 2011 Elsevier Ltd. A doi:10.1016/j.microrel.2011.12.020 ⇑ Corresponding author. Tel.: +82 42 350 3375; fax E-mail address: [email protected] (K.-W. Paik). Various fine pitch chip-on-film (COF) packages assembled by (1) anisotropic conductive film (ACF), (2) nonconductive film (NCF), and (3) AuSn metallurgical bonding methods using fine pitch flexible printed circuits (FPCs) with two-metal layers were investigated in terms of electrical characteristics, flip chip joint properties, peel adhesion strength, heat dissipation capability, and reliability. Two-metal layer FPCs and display driver IC (DDI) chips with 35 lm, 25 lm, and 20 lm pitch were prepared. All the COF packages using two-metal layer FPCs assembled by three bonding methods showed stable flip chip joint shapes, stable bump contact resistances below 5 mX, good adhesion strength of more than 600 gf/cm, and enhanced heat dissipation capability compared to a conventional COF package using one-metal layer FPCs. A high temperature/humidity test (85 C/85% RH, 1000 h) and thermal cycling test (T/C test, 40 C to + 125 C, 1000 cycles) were conducted to verify the reliability of the various COF packages using twometal layer FPCs. All the COF packages showed excellent high temperature/humidity and T/C reliability, however, electrically shorted joints were observed during reliability tests only at the ACF joints with 20 lm pitch. Therefore, for less than 20 lm pitch COF packages, NCF adhesive bonding and AuSn metallurgical bonding methods are recommended, while all the ACF and NCF adhesives bonding and AuSn metallurgical bonding methods can be applied for over 25 lm pitch COF applications. Furthermore, we were also able to demonstrate double-side COF using two-metal layer FPCs. 2011 Elsevier Ltd. All rights reserved.