• Journal of Welding and Joining
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• v.29 no.1
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• pp.99-106
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• 2011

Joint strength between a solder ball and a pad on a substrate is one of the major factors which have effects on electronic device reliability. The effort to improve solder joint strength via surface cleaning, heat treatment and solder composition change have been in progress. This paper will discuss the method of solder ball joint strength improvement using LF hydrogen radical cleaning treatment and focus on the effects of surface treatment condition on the solder ball shear strength and interfacial reactions. In the joint without radical cleaning, voids were observed at the interface. However, the specimens cleaned by hydrogen-radical didn't have voids at the interface regardless of cleaning time. The shear strength between the solder ball and the pad was increased over 120%(about 800gf) when compared to that without the radical treatment (680gf) under the same reflow condition. Especially, at the specimen treated for 5minutes, ball shear strength was considerably increased over 150%(1150gf). Through the observation of fracture surface and cross-section microstructure, the increase of joint strength resulted from the change of fracture mode, that is, from the solder ball fracture to IMC/Ni(P) interfacial fracture. The other cases like radical treated specimen for 1, 3, 7, 9min. showed IMC/solder interfacial fracture rather than fracture in the solder ball.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2007.04a
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• pp.67-79
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• 2007

• Journal of the Korean Society of Safety
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• v.25 no.6
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• pp.14-21
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• 2010

A miniature single solder ball joint is designed to mimic the actual solder joints used in the micro-electric industries. Shear tests were conducted to evaluate the mechanical behavior of miniature single solder joints at intermediate strain rates from $0.019\;s^{-1}$ to $2.16\;s^{-1}$ at room temperature. The shear fracture strength of the present solder ball joints generally increased with increasing shear strain rate, ranging from 32 to 51MPa. This behavior is affected by the sensitivity of bulk solder strength to strain rate. Shear fracture mode changed from brittle to partial ductile (failure inside the bulk solder) with an increase of shear speed. The unloading shear fracture toughness is generally consistent with the measure of the amount of bulk solder on the fractured surface.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2001.11a
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• pp.67-73
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• 2001

To investigate the relationships of solder joint characteristics with solder composition and A:V ratio (solder volume per pad area), Sn-37Pb and Sn-4.0Ag-0.5Cu solder balls with 330, 400, 450 and $457{\mu}{\textrm}{m}$ size were reflowed on same substrate. Sn-37Pb and Sn-4.0Ag-0.5Cu was reflowed at $220^{\circ}C$ and $240^{\circ}C$ respectively by IR-type soldering machine. As a result of reflowed solder- ball diameter(D) and height(H) measurement, D/H was decreased with solder ball size increment in range of 330~450 ${\mu}{\textrm}{m}$. But, D/H was increased in the solder joint for 457 ${\mu}{\textrm}{m}$ size, it was caused possibly by decrement of solder ball height increment compared with solder volume increment. As a result of shear and pull test, joint strength with A:V ratio was high. Joint strength of Sn-4.0Ag-0.5Cu was higher than Sn-37Pb. However, Sn-37Pb had more stable solder joint of small standard deviation. A thick and clean scallop type Ni-Cu-Sn intermetallic compound layer was formed in high A:V ratio and Sn-4.0Ag-0.5Cu solder joint interface.

• Journal of Welding and Joining
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• v.21 no.3
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• pp.92-98
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• 2003

This paper describes the numerical prediction of the thermal fatigue life of a $\mu$BGA(Micro Ball Grid Array) solder joint. Finite element analysis(FEA) was employed to simulate thermal cycling loading for solder joint reliability. Strain values, along with the result of mechanical fatigue tests for solder alloys were then used to predict the solder joint fatigue life using the Coffin-Manson equation. The results show that Sn-3.5mass%Ag solder had the longest thermal fatigue life in low cycle fatigue. Also a practical correlation for the prediction of the thermal fatigue life was suggested by using the dimensionless variable ${\gamma}$, which was possible to use several lead free solder alloys for prediction of thermal fatigue life. Furthermore, when the contact angle of the ball and chip has 50 degrees, solder joint has longest fatigue life.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.630-633
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• 2004

Generally, component and FR-4 board are connected by solder joint. Because material properties of components and FR-4 board are different, component and FR-4 board show different coefficients of thermal expansion (CTE) and thus strains in component and board are different when they are heated. That is, the differences in CTE of component and FR-4 board cause the dissimilarity in shear strain and BGA solder joint s failure. The first order Taylor series expansion of the limit state function incorporating with thermal fatigue models is used in order to estimate the failure probability of solder joints under heated condition. A model based on plastic-strain rate such as the Coffin-Manson Fatigue Model is utilized in this study. The effects of random variables such as frequency, maximum temperature, and temperature variations on the failure probability of the BGA solder joint are systematically investigated by using a failure probability model with the first order reliability method(FORM).

• Journal of Welding and Joining
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• v.20 no.2
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• pp.90-94
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• 2002

FC-BGA has advantages over other interconnection methods including high I/O counts, better electrical performance, high throughput, and low profile. But, FC-BGA has a lot of reliability issues. The 2nd level solder joint reliability of the FC-BGA with large chip on laminate substrate was studied in this paper. The purpose of this study is to discuss solder joint failures of 2nd level thermal cycling test. This work has been done to understand the influence of the structure of package, the properties of underfill, the properties and thickness of bismaleimide tiazine substrate and the temperature range of thermal cycling on 2nd level solder joint reliability. The increase of bismaleimide tiazine substrate thickness applied to low modulus underfill was improve of solder joint reliability. The resistance of solder ball fatigue was increased solder ball size in the solder joints of FC-BGA.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.3
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• pp.31-36
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• 2002

The 2nd level solder joint reliability of 153 FC-BGA for high-speed SRAM (Static Random Access Memory) with the large chip on laminate substrate comparing to PBGA(Plastic Ball Grid Array) was studied in this paper. This work has been done to understand an influence as the mounting with single side or double sides, structure of package, properties of underfill, properties and thickness of substrate and size of solder ball on the thermal cycling test. It was confirmed that thickness of BT(bismaleimide tiazine) substrate increased from 0.95 mm to 1.20 mm and solder joint fatigue life improved about 30% in the underfill with the low young's modulus. And resistance against the solder ball crack became twice with an increase of the solder ball size from 0.76 mm to 0.89 mm in solder joints.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1207-1208
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• 2006

We developed the copper core ball electroplated with Sn-Ag-Cu of the eutectic composition which used mostly as Pb free solder ball with high reliability. In order to search for the practicality of this developed copper core ball, the evaluation was executed by measuring the initial joint strength of the sample mounted on the substrate and reflowed and by measuring the joint strength of the sample after the high temperature leaving test and the constant temperature and the humidity leaving test. This evaluation was compered with those of the usual other copper core balls electroplated with (Sn,Sn-Ag,Sn-Cu,Sn-Bi) and the Sn-Ag-Cu solder ball.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.74-74
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• 2009

카본나노튜브(CNT) 복합체는 우수한 기계적 성질을 가지고 있어 다양한 분야에서 연구되고 있다. 본 연구에서는 카본나노튜브(CNT)를 간단한 볼밀공정을 사용하여 Sn3.5Ag solder ball과 SAC305 powder 표면에 혼합하고 이를 통해 접합부 특성을 관찰하였다. 볼밀을 실시하기 전 카본나노튜브(CNT)는 초음파을 이용하여 분산을 실시하였다. Sn3.5Ag solder ball의 직경은 450um이고 SAC305 powder의 직경은 약 30um이었으며 이때 사용한 볼밀볼의 직경은 각각 3mm, 1mm이다. 볼밀 회전속도는 약 300rpm이고 6, 12, 18, 24시간동안 볼밀을 실시하였다. 24시간 볼밀 후에도 solder ball과 solder powder의 모양은 크게 변하지 않았다. SEM을 통해 표면을 관찰한 결과 분산된 카본나노튜브(CNT)는 solder ball과 solder powder의 표면에서 관찰되었다. 카본나노튜브(CNT)가 삽입된 solder ball은 BGA coupon 위에 놓고 Reflow를 실시하여 접합하였고 solder powder은 flux를 첨가하여 paste로 제조하여 2012 chip에 대한 접합특성을 관찰하였다. 카본나노튜브(CNT)는 solder ball 내부의 표면근처에서 관찰되었으며 카본나노튜브(CNT)가 혼합된 solder ball은 Aging 실시 후에 IMC 두께가 카본나노튜브(CNT)가 혼합되지 않은 solder ball에 비해 두께가 작고 접합강도는 약 10% 증가하였다. 또한 카본나노튜브(CNT)가 혼합된 solder paste와 카본나노튜브(CNT)가 혼합되지 않은 solder paste를 비교한 결과 인쇄성은 모두 양호하였으며 카본나노튜브(CNT)가 혼합된 paste를 사용한 chip의 전단강도가 높게 나타났다.