Electric Properties of Connections by Anisotropic Conductive Film

Choi

IEEE Trans. Compon., Packag. Manufact. Technol.

et al. 2015

In this paper, a thermal acid generator was added as a flux activator in solder anisotropic conductive films (ACFs) to eliminate solder oxide resulting in stable solder wetting on metal pads. Since the native solder oxide causes poor wettability of the solder particles, solder oxide was chemically removed by the flux activator in solder ACFs. The test vehicles consisted of polyimidebased flexible printed circuits and FR-4 organic rigid printed circuit boards, which have 300-µm pitch Cu pads with electroless nickel immersion gold metal surface finish. The thickness of the solder incorporated ACFs were 50 µm and it consists of epoxy-based adhesive resin, 20 wt% of 5-15-µm diameter SAC305 (96.5Sn-3.0Ag-0.5Cu) solder particle, flux activator, and 5 wt% of 5-µm diameter Au-coated Ni particles, which act as a spacers to maintain a stable gap between metal pads. According to the experimental results, solder wettability improved significantly, as the amount of the flux activator increased in the solder ACFs due to solder oxide removal. As a result, the flux activator caused significant improvement of electrical properties of solder ACF joints, such as contact resistance, power handling capability, and reliability. Therefore, the flux activator added solder ACFs can provide an excellent interconnection method for high-power flex-on-board and flex-on-flex assemblies.

Section: A Estimation Of the Flux Activator Concentration For The Oxmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Flux Activators on the Solder Wettability of Solder Anisotropic Conductive Films

Choi

IEEE Trans. Compon., Packag. Manufact. Technol.

et al. 2015

4th International Conference on Adhesive Joining and Coating Technology in Electronics Manufacturing. Proceedings. Presented At

“…A 40% compression level of the particle was reported to have a highly stable resistance in 85"C/85RH%. [4].…”

Section: Planaritymentioning

confidence: 99%

Anisotropic conductive adhesive films for flip chip on flex packages

Fang²

Miniaturization and high performance demand more and more flip chip and chip scale packages for consumer products. New packages require increased functionality with a reduction in overall size and weight. The traditional flip chip approaches using solder bumps pose an unacceptably high cost for lowend consumer products. Package technologies for integrated circuits with low to moderate I/O counts (below 150) are critical. A low cost and low profile flip chip on flex CSP package using anisotropic conductive adhesive film (ACF) was developed. This package has the flexibility to use the existing wire bonding pad configuration without adding prohibitive redistribution and wafer solder bumping costs, and also eliminates the need for under-chip encapsulation. Figure 1 : Package top and bottom view. Material research and evaluations were conducted to optimize the adhesive material for flip chip on flex applications. Anisotropic conductive adhesive film bonding processes were developed through design of experiments. Critical bonding equipment parameters and process conditions were identified. ACF bonding quality was characterized to adjust the bonding equipment co-planarity. A double layer epoxy film with the second layer loaded with Au plated polymer spheres was identified to be the best ACF material. Contact resistances of the ACF joints were monitored though multiple reflow and thermal-mechanical shock cycles. Various volume production approaches were also explored.

4th IEEE International Conference on Polymers and Adhesives in Microelectronics and Photonics, 2004. POLYTRONIC 2004.

“…[6,7], however relatively few studies have addressed the second topic e.g. [8,9]. These studies have mainly focused on estimating the contact constriction resistances between the particles and conductors.…”

Section: Introductionmentioning

confidence: 99%

“…Open circuits may result when metal coated particles are compressed by more than 33% (kXl.33) of their original size, while intermediate resistances occur at less than 20% compression [16]. The most stable values of resistance have been reported for a transformation degree of 40% for metal coated particles [8,17]. However, for solid particle such values of k for a low and stable resistance have not been reported.…”

mentioning

confidence: 99%

Electrical conduction characteristics of solid metal anisotropic conductive adhesive particles

Don

Whalley²,

Liu³

Anisotropic Conductive Adhesives (ACAs) have been used in fine pitch electronics packaging for over a decade and provide a high density and low temperature bonding method in a range of niche applications. In an ACA assembly, individual particles act as electrical conductors, providing current paths for fine pitch electronics interconnections. This paper presents a model of the electrical conduction