Major electric device makers have launched foldable mobile phones, tablets, and laptops since 2020. At that time, foldable display is a key feature of foldable devices. In this year, the device makers want to add more different function to foldable devices, and the key feature of brand-new foldable devices is to provide reliable water resistance.

Typically, the foldable device consists of two electrical bodies, which have Application Processor (AP), memory on board, camera electronic boards, speaker, microphone, battery and so on. Each electronic part in two bodies should be connected by bridging FPCB (Flexible Printed Circuit Board).

Two main bodies of the fold device adopted exiting waterproof technology. However, there was big challenge to give waterproof function in FPCB connecting area in the hinge part, because FPCB connecting area should have macro / micro gaps, where water could be seeped.

DOWSIL™ SE-9171 / 9173 Adhesive has been applied to FPCB connecting area in the hinge part to fill the gap between the connecting part and bridge FPCB to protect the inner electronic parts against seeping water. To make the foldable phone provide great water resistance, The sealing adhesive was required to have reliable adhesion performance onto customized hinge surface. And UV curability and repairability are also key requirement to provide great processability and high yield.

DOWSIL™ SE-9171 / 9173 Adhesive is dual (UV cure with secondary moisture cure) curable Si adhesive. SE-9171 is enabled to cure by UV irradiation and enhanced mechanical property and shadow area cure by secondary moisture cure reaction. Its instant cure property by UV radical reaction enables to remove bottle-neck step caused by delayed curing time from conventional moisture cure or heat curable product in the manufacturer's process. And it helps to reduce energy consumption compared to heat curable product. Enhanced adhesion performance and repairable adhesion property provides high credibility to device and contributes to longer life, resulting in fewer waste and enabling re-use of failed units. Thus, it can contribute overall cost beneficial of manufacturing as well as environment.

For excellent curing performance with high adhesion in shadow area, secondary moisture cure technology is used in DOWSIL™ SE-9171 / 9173 Adhesive. Dow found that the ratio of UV cure part to moisture cure part was critical for maintaining affordable mechanical property with enhanced adhesion performance and repairable adhesion in FPCB connecting area. For example, high content of UV cure part affects to high modulus after UV irradiation. Then, this high modulus brings about waterproofness failure due to easy delamination. Therefore, lowering modulus through cross linking density by optimum ratio of UV cure part to moisture cure part provides affordable performance for waterproofness in this FPCB connecting area.

These performance advantages allow consumers to develop a variety of foldable electronics with DOWSIL™ SE-9171 / 9173 Adhesive.