Novel Material for High Layer Count, High Rel PCBs
Paper reviews laminate systems developed to face the increasing physical demands of withstanding lead-free soldering processes.
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Authored By:
Jie Wan, Junqi Tang, Xianping Zeng
Shengyi Technology Co., Ltd.
Dongguan, Guangdong, China
Summary
Over the past few years a new family of laminate systems has been developed to face the increasing physical demands ofbwithstanding Pb-free soldering processes used in the assembly of RoHS compliant products. Many of the materials have been found to perform satisfactorily for consumer type products where reflow temperatures peak around 245C. However the highbend PWB designs for the telecommunications and IT equipments typically tend to be more complex, thicker and therefore have a much higher thermal mass than consumer products.
In order to apply sufficient heat to enable satisfactory solder
reflow of surface mounted devices, the temperature of the printed wiring board can peak at up to 260C. Add to that the complexity of the board (typically double side assembled) and the requirement to be able to repair boards, then it is highly possible that boards throughout their manufacturing cycle could see up to 5 thermal excursions up to this 260C level withstanding 20~30 seconds over 255C. The ability of laminate systems to withstand the combined thermal exposure without degradation or delamination and at the same time exhibiting consistent electrical properties is essential.
To meet the demand, a novel thermoplastic resin modified multifunctional epoxy system material has been developed. Silica fillers have been carefully selected for ensuring the lower CTE. The material shows an outstanding heat resistance, reliability and toughness performance with complex BGA design (Pitch 0.8mm, through hole diameter 0.25mm) on thicker (Thickness: 4mm PTH board and 3.2mm HDI board) PWB board comparing with currently available Pb -Free compatible materials. The dielectric properties and other properties of this material will be presented.
Conclusions
A novel thermoplastic resin modified mult ifunctional epoxy system material has been developed. The material shows an outstanding heat resistance, reliability and toughness performance with complex BGA design (Pitch 0.8mm, through holebdiameter 0.25mm) on thicker (Thickness: 4mm PTH board and 3.2mm HDI board) PWB board comparing with currentlybavailable Pb-Free compatible materials. The dielectric properties of this novel would able to get Dk 4.2 and Df 0.015 under
1GHz by SPDR method.
Initially Published in the IPC Proceedings
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