Abstract
Micron sizes solder metallurgical joints have been applied in a thin film application of anisotropic conductive film and benefited three general advantages, such as lower joint resistance, higher power handling capability, and reliability, when compared with pressure based contact of metal conductor balls. Recently, flex-on-board interconnection has become more and more popular for mobile electronic applications. However, crack formation of the solder joint crack was occurred at low temperature curable acrylic polymer resins after bonding processes. In this study, the mechanism of SnBi58 solder joint crack at low temperature curable acrylic adhesive was investigated. In addition, SnBi58 solder joint cracks can be significantly removed by increasing the storage modulus of adhesives instead of coefficient of thermal expansion. The first approach of reducing the amount of polymer rebound can be achieved by using an ultrasonic bonding method to maintain a bonding pressure on the SnBi58 solder joints cooling to room temperature. The second approach is to increase storage modulus of adhesives by adding silica filler into acrylic polymer resins to prevent the solder joint from cracking. Finally, excellent acrylic based SnBi58 solder joints reliability were obtained after 1000 cycles thermal cycling test.
Highlights
Amid the current trend for wearable electronics assembly, flex-on-board (FOB) assembly is attracting a greater attention because of its important role in replacing conventional physical contacts-based socket type interconnections
Polymer resin was cured by◦ the heat bondingparameters parameters(peak were set200 as 200
The significance of this research is to present the low resin modulus is the determined factor to cause solder joint cracks, we provided two methods to resin prevent solder joint from cracking byfactor
Summary
Amid the current trend for wearable electronics assembly, flex-on-board (FOB) assembly is attracting a greater attention because of its important role in replacing conventional physical contacts-based socket type interconnections. In the case of conventional socket type interconnections, there are three main drawbacks, which include: physical contact, large package size, and low packaging density [1]. For reducing the package thickness from 4 mm to 0.1 mm, and fine pitch capability to less than 100 μm, FOB application, as shown, is an obvious choice in the replacement of conventional socket type interconnections [2]. Bondingprocess process and and formed formed flex-on-board. The anisotropicFigure conductive films (ACFs) are theflex-on-board interconnection materials to assembly FOB
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