高導電性錫球與膠材對WLCSP技術之最佳化設計

Optimal Design of a High Conductivity Solder Ball and Underfill Technology for Wafer Level Chip Scale Package

劉孟宗(Meng-Tzung Liu)

指導教授 ： 莊為群

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/碩士(2012年)

摘要

晶圓級尺度封裝 (Wafer Level Chip Scale Package; WLCSP), 因為

具有高效能、 高功率與高密度等優點, 逐漸成為未來發展的趨勢。 雖然WLCSP

封裝體的電子訊號I/O密度得以提升, 但是可靠度卻較低。 雖然影嚮封裝體可靠度

的原因較多, 其中又以錫球與膠材為主要的的關鍵。

本研究採用SnAg無鉛錫球的WLCSP封裝體, 先預測錫球?銲後的形狀與高度;

使用Pro-E建立三維模型, 再利用Ansys 10.0 Workbench有限元素分析軟體

分析可靠度, 以瞭解封裝體在受溫度循環負荷下的變形、 錫球應力應變等行為的

變化情形。 並將實驗後之產品與Ansys軟體分析可靠度比較、 修正。

應用有限元素分析 (Ansys), 研究以高導電性錫膠對WLCSP封裝技術的最佳化

設計分析, 並考慮整體的翹曲 (Global Warpage)、 錫球內的最大剪應力

(Maximum Shear Stress)和應力緩衝層的最大剪應力,為最佳化之回饋因子。

WLCSP的幾何形狀包括晶片厚度、 焊墊直徑、 錫球的高度、 應力緩衝層的

楊氏係數 (Young Modulus)和熱膨脹係數 (CTE), 這些都是實驗設計

(Design of Experiment, D.O.E.)考慮的因子; 以提高封裝體的疲勞壽命。

使用應力緩衝層 (Compliant Layer)的WLCSP與傳統覆晶封裝 (Flip-

Chip)比較, 得知此種應力緩衝層, 能有效釋放應力和降低成本兩大優勢。

應用有限元素分析軟體來分析降低整體翹曲和剪應力; 並可協助得到最佳的整體

翹曲、 降低錫球內所受的剪應力(Shear Stress)和應力緩衝層所受的剪應力都

達到最佳化的結果, 及有效提升封裝體的可靠度。

在微電子構裝技術爆炸性成長的時代, 高I/O、 高密度和可靠的訊號連接,

為IC封裝業界主要考慮的因素, 因此許多封裝的技術型式被發展出來, 像球狀

陣列 (BGA)封裝技術、 晶片尺度封裝 (CSP)技術、 覆晶 (Flip chip)封裝

技術、 晶圓級尺度封裝 (WLCSP)技術等等。

所以我希望透過本論文之完成, 能提供業界對無鉛錫球與膠材材料的WLCSP封裝

體的應用有更深一層的認識。 降低WLCSP封裝體的成本與提高封裝體的可靠度,

並減短研發時間, 提昇產品的競爭力。

關鍵字

晶圓級尺度封裝 ； 有限元素分析軟體 ； 應力應變 ； 整體翹曲 ； 剪應力 ； 應力緩衝層 ； 楊氏係數 ； 熱膨脹係數 ； 實驗設計 ； 覆晶 ； 部份實驗因子 ； 球狀陣列封裝技術 ； 晶片尺度封裝技術 ； 覆晶封裝技術 ； 晶圓級尺度封裝技術。

並列摘要

The high efficiency, high power and high density have

caused the development of the Wafer Level Chip Scale Package

(WLCSP) to be the trend in the future. Although the input

and output density of the WLCSP electronic signal can be

improved, but also causes the reliability to reduce.

Although there are many factors affecting the reliability

of the package, among which those related to the underfill

and the solder ball are considered to be the key factor.

This paper focuses on Sn (96.5) / Ag (3.5) lead-free

solder ball in WLCSP package. First, predict the shape and

height of the solder ball then utilize Pro-E software to

build up a three-dimensional model, and with the use of

finite element analysis ANSYS 10.0 Workbench to investigate

deformations of entire package under thermal cycling, and

changes of stress-strain curve for solder ball and the

package further comparing between the product reliability

and Ansys software simulation.

Using finite element analysis (Ansys) to research the high

conductivity of the solder ball and its underfill and have

the best design for the WLCSP package. And also consider the

overall warpage, the maximum solder ball shear force, the

stress buffer layer shear stress as the best feedback

factors.

The different WLCSP geometry, including chip thickness,

pad diameter, solder ball height, the stress buffer layer

Young’s modulus and the coefficient of thermal expansion

(CTE) these are the experimental design (Design of

Experiment, DOE) to consider the factors then to improve

the stress and life of WLCSP package.

The comparison between the compliant layer of the WLCSP

and the traditional flip-chip package and then find out all

the stress buffer layer thus creating two advantages in

effectively release the stress and also cost down.

In reference to finite element analysis to predict lower

overall warpage and shear stress. It also helps to get the

best overall warping; reducing the solder ball shear stress

and the stress buffer layer suffered shear stress further

optimizing to achieve results, and effective body to enhance

the package reliability.

The microelectronics packaging technology era have

explosive growth that high I/O, high density and reliability

signal connections for the IC packaging industry which

became the main considerations. Therefore many different

types of packaging techniques have been developed, such as

BGA (Ball Grid Array) packaging technology, CSP (Chip Scale

Package) packaging technology, FC (Flip Chip) packaging

technology, WLCSP (Wafer Level Chip Scale Package)

packaging technology and so on.

I hope that through the study of this paper, it could be

a help to the packaging industry for the application of

lead-free solder ball material and underfill material,

hopefully cutting cost, enhancing WLCSP reliability, and

shortening development time, and enhance the competitive

of the WLCSP products.

並列關鍵字

WLCSP ； Pro-E ； Finite Element Analysis ； Ansys ； Stress-Strain ； Overall Warpage ； Shear Force ； Stress Buffer Layer ； Young Modulus ； CTE ； DOE ； Compliant Layer ； Flip Chip ； Part of the Experimental Factor ； BGA ； CSP ； FC.

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