Electrical Characterization of NCP- and NCF-Bonded Fine-Pitch Flip-Chip-on-Flexible Packages

Abstract

Electronic portable devices are aimed towards higher response speed with a better viewing resolution display. Nonconductive paste (NCP) and nonconductive film (NCF) are the adhesive materials used in fine-pitch display applications. This study compares two commercially available adhesives for fine-pitch chip-on-flex (COF) applications. The electrical performance of the NCP-bonded COF was better compared to the NCF. The rheological properties of these materials in the initial stages and the mechanical properties of the adhesives after bonding are claimed to be the main factors. The semisolid form of the NCF which melts and flows slowly from the interconnection joints finally reduced the effective contact area in the joint as compared to the NCP. A low-pressure bonding caused entrapment of adhesive in the joints, induced stress accumulation in the -direction during high thermal loading, and a high coefficient of thermal expansion (CTE) mismatch in between bumps, adhesive, and electrode traces on the flexible substrate were the key factors for the degradation of electrical conductivity. A high load of 100 N and above was recommended since the effective contact area built into the interconnection was good and reliable after 400 cycles of a thermal shock test of 55 C-125 C. The NCP with a higher elastic modulus which ensures higher stiffness and stability towards elongation gave a better reliability in this environmental test. Cross sectioning and SEM analysis provide evidence of the effective contact area of the joint before and after the thermal cycle environmental test.

Microjoining of LSI Chips on Poly(ethylene naphthalate) Using Compliant Bump

“…On the other hand, there are several kinds of chip-on-film (COF) technology to bond LSI chips to flexible substrates, such as solder joining, 8,9) anisotropic-conductive film (ACF), [10][11][12][13] and nonconductive adhesive (NCA). 14,15) Recently, techniques for integrating thin Si chips in high-T g materials such as PI have been developed by using these bonding technologies. 10,16) However, these bonding technologies cannot be applied to low-T g materials such as PEN, because the temperature required for bonding is more than 200 C.…”

Thermo-Compression Bonding of Cu/SnAg Pillar Bumps with Electroless Palladium Immersion Gold (EPIG) Surface Finish

“…The rough surfaces of the EPIG surface finishes had more dimples and valleys than that of the ENEPIG surface finish. These dimples and valleys finally become the entrapment sites for the filler and resin during the bonding process [ 22 ].…”

Mechanical Reliability Assessment of a Flexible Package Fabricated Using Laser-Assisted Bonding

“…In addition, the solidified solder bump formed after bonding is brittle and very fragile, making it vulnerable to bending stress. Therefore, various advanced bonding technologies and bonding materials were recently developed, involving the use of non-conductive paste (NCP) [ 15 ], anisotropic conductive film (ACF) [ 16 , 17 ], and anisotropic conductive paste (ACP) [ 18 , 19 ] materials. Recently, thermo-compression bonding [ 20 ], ultrasonic bonding [ 21 ], and laser bonding technologies [ 22 ] were also developed in place of the mass-reflow bonding method and are now widely used in the flexible materials industries to lower the bonding temperature and to realize uniform and stable bonding.…”