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수치해석을 이용한 팬 아웃 웨이퍼 레벨 패키지의 휨 경향 및 신뢰성 연구

Numerical Analysis of Warpage and Reliability of Fan-out Wafer Level Package

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키워드

주제분류재료공학

초록

최근 모바일 응용 제품에 사용되는 반도체 패키지는 고밀도, 초소형 및 다기능을 요구하고 있다. 기존의 웨이퍼 레벨 패키지(wafer level package, WLP)는 fan-in 형태로, I/O 단자가 많은 칩에 사용하기에는 한계가 있다. 따라서 팬아웃 웨이퍼 레벨 패키지(fan-out wafer level package, FOWLP)가 새로운 기술로 부각되고 있다. FOWLP에서 가장 심각한 문제 중의 하나는 휨(warpage)의 발생으로, 이는 FOWLP의 두께가 기존 패키지에 비하여 얇고, 다이 레벨 패키지 보다휨의 크기가 매우 크기 때문이다. 휨의 발생은 후속 공정의 수율 및 웨이퍼 핸들링에 영향을 미친다. 본 연구에서는 FOWLP의 휨의 특성과 휨에 영향을 미치는 주요 인자에 대해서 수치해석을 이용하여 분석하였다. 휨을 최소화하기 위하여 여러종류의 epoxy mold compound (EMC) 및 캐리어 재질을 사용하였을 경우에 대해서 휨의 크기를 비교하였다. 또한 FOWLP의 주요 공정인 EMC 몰딩 후, 그리고 캐리어 분리(detachment) 공정 후의 휨의 크기를 각각 해석하였다. 해석 결과, EMC몰딩 후에 발생한 휨에 가장 영향을 미치는 인자는 EMC의 CTE이며, EMC의 CTE를 낮추거나 Tg(유리천이온도)를 높임으로서 휨을 감소시킬 수 있다. 캐리어 재질로는 Alloy42 재질이 가장 낮은 휨을 보였으며, 따라서 가격, 산화 문제, 열전달 문제를 고려하여 볼 때 Alloy 42 혹은 SUS 재질이 캐리어로서 적합할 것으로 판단된다.

Abstract

For mobile application, semiconductor packages are increasingly moving toward high density, miniaturization,lighter and multi-functions. Typical wafer level packages (WLP) is fan-in design, it can not meet high I/O requirement. The fan-out wafer level packages (FOWLPs) with reconfiguration technology have recently emerged as a new WLPtechnology. In FOWLP, warpage is one of the most critical issues since the thickness of FOWLP is thinner than traditionalIC package and warpage of WLP is much larger than the die level package. Warpage affects the throughput and yieldof the next manufacturing process as well as wafer handling and fabrication processability. In this study, we investigatedthe characteristics of warpage and main parameters which affect the warpage deformation of FOWLP using the finiteelement numerical simulation. In order to minimize the warpage, the characteristics of warpage for various epoxy moldcompounds (EMCs) and carrier materials are investigated, and DOE optimization is also performed. In particular, warpageafter EMC molding and after carrier detachment process were analyzed respectively. The simulation results indicate thatthe most influential factor on warpage is CTE of EMC after molding process. EMC material of low CTE and high Tg(glass transition temperature) will reduce the warpage. For carrier material, Alloy42 shows the lowest warpage. Therefore,considering the cost, oxidation and thermal conductivity, Alloy42 or SUS304 is recommend for a carrier material.

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