• Journal of the Microelectronics and Packaging Society
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• v.17 no.1
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• pp.25-31
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• 2010

In this study, we investigated the morphology and thermal stability of interfacial phases in joint between lead free solder(Sn-3.0Ag-0.5Cu) and electroless Ni-W-P under bump metallizations(UBM) with different tungsten contents as a function of thermal aging. Content of phosphorus of each deposits was fixed at 8 wt.%, and content of tungsten was variated each 0, 3, 6 and 9 wt.%. Specimens were prepared by reflowing at $255^{\circ}C$, aging range was $200^{\circ}C$ and up to 2 weeks. After reflow process, in the electroless Ni(W)-P/solder joint, the interfacial intermetallic compound(IMC) was showed both $(Cu,Ni)_6Sn_5$ and $(Ni,Cu)_3Sn_4$. UBM and generated IMC at the interface of lead free solder was proportionally increased with aging time. The thickness of IMC was increased because the generation rate of $Ni(W)_3P$ decreased with increasing contents of W.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.81-88
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• 2019

In this study, the effects of graphene oxide (GO) addition on electromigration (EM) lifetime of Sn-3.0Ag-0.5Cu Pb-free solder joint between a ball grid array (BGA) package and printed circuit board (PCB) were investigated. After as-bonded, $(Cu,Ni)_6Sn_5$ intermetallic compound (IMC) was formed at the interface of package side finished with electroplated Ni/Au, while $Cu_6Sn_5$ IMC was formed at the interface of OSP-treated PCB side. Mean time to failure of solder joint without GO solder joint under $130^{\circ}C$ with a current density of $1.0{\times}10^3A/cm^2$ was 189.9 hrs and that with GO was 367.1 hrs. EM open failure was occurred at the interface of PCB side with smaller pad diameter than that of package side due to Cu consumption by electrons flow. Meanwhile, we observed that the added GO was distributed at the interface between $Cu_6Sn_5$ IMC and solder. Therefore, we assumed that EM reliability of solder joint with GO was superior to that of without GO by suppressing the Cu diffusion at current crowding regions.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.3
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• pp.55-62
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• 2001

With a spread of BGA, CSP and fine pitch devices, the need of flatter surface finish in bare board is becoming more critical in solderability. The electroless Ni/Au plating has a solution of these needs and also has being spread to apply to surface finish for bare board in many electronic goods. But, the electroless Ni/Au plating had several issues such as Ni oxidation and phosphorous contents. Before this study, we studied on the effect of BGA solderability in electroless Ni/Au plating and chose some major factors such as the oxidation property of NiP plating and warpage of board. Firstly, we made test board with various plating conditions and improved the plating property through the improvement of NiP oxidation reducing P content. Also, we minimized the warpage of board with the improvement of inner layer structure and the analysis of warpage. For the evaluation of solderability, we analyzed the warpage of board and the plating property after mounting BGA on the board with optimizing conditions. The solder joint of BGA is investigated by SEM(Scanning Electronic Microscope) and OM(Optical Microscope). The composition of joint is used by EDS(Energy Dispersive Spectroscopy). We analyzed the fracture strength and mode by ball shear teser.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.183-188
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• 2002

With the contact pad consisted of $0.5{\mu}{\textrm}{m}$ $Au/5{\mu}{\textrm}{m}$ Ni/Cu layers on a conventional ball grid array(BGA) substrate, metallurgical reaction properties between the pad and In-15(wt.%)Pb-5Ag solder alloy were studied after reflow and solid aging. In as-reflow condition, thin AuIn$_2$or Ni$_{28}$In$_{72}$ intermetallic layer was formed at the solder/pad interface according to reflow time. Dissolution of the Au layer into the molten solder was remarkably limited in comparison with eutectic Sn-37Pb alloy. After solid aging of 300 hrs, thickness of In-Ni layer increased to about $2{\mu}{\textrm}{m}$ in the both as-reflow case. It was observed that In atoms diffuse through the AuIn$_2$phase to react with underlaying Ni layer. The metallurgical reaction properties between In-l5Pb-7Ag alloy and Au/Ni surface finish were analysed to result in suppression of Au-embrittlement in the solder joints.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.4
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• pp.1-7
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• 2006

A major failure mode for wafer level chip size package (WLCSP) is thermo-mechanical fatigue of solder joints. The mechanical strains and stresses generated by the coefficient of thermal expansion (CTE) mismatch between the die and printed circuit board (PCB) are usually the driving force for fatigue crack initiation and propagation to failure. In a WLCSP process peripheral or central bond pads from the die are redistributed into an area away using an insulating polymer layer and a redistribution metal layer, and the insulating polymer layer affects solder joints reliability by absorption of stresses generated by CTE mismatch. In this study, several insulating polymer materials were applied to WLCSP to investigate the effect of insulating material. It was found that the effect of property of insulating material on WLCSP reliability was altered with a solder ball layout of package.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.4
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• pp.17-25
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• 2006

Thermo-mechanical behavior of flip-chip plastic ball grid array (FC-PBGA) packages are characterized by high sensitive $moir\'{e}$ interferometry. $Moir\'{e}$ fringe patterns are recorded and analyzed for several temperatures. Deformation analysis of bending displacements of the packages and average strains in the solder balls for both single and double-sided package assemblies are presented. The bending displacement of the double-sided package assembly is smaller than that of the single-sided one because of its symmetric structure. The largest effective strain occurred at the solder ball located on the edge of the chip and its magnitude of the double-sided package assembly is greater than that of single-sided one by 50%.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.38-44
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• 2008

The micro-structural changes, strength characteristics, and micro-fractural behaviors at the joint interface between a Sn-4.0wt%Ag-0.5wt%Cu solder ball and UBM treated by isothermal aging are reported. From the reflow process for the joint interface, a small amount of intermetallic compound was formed. With an increase in the isothermal aging time, the type and amount of the intermetallic compound changed. The interface without an isothermal treatment showed a ductile fracture. However, with an increase in the aging time, a brittle fracture occurred on the interface due mainly to the increase in the size of the intermetallic compounds and voids. As a result, a drastic degradation in the shear strength was observed. From a microshear test by a scanning electron microscope, the generation of micro-cracks was initiated from the voids at the joint interface. They propagated along the same interface, resulting in coalescence with neighboring cracks into larger cracks. With an increase in the aging time, the generation of the micro-structural cracks was enhanced and the degree of propagation also accelerated.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.98-103
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• 2002

BGA(Ball Grid Array) 패키지의 솔더볼 패드 중의 하나인 Au/Ni-Co/Cu 금속층 위에 Bi가 첨가된 Sn-3.5Ag-$\chi$Bi 솔더볼을 리플로우시켰다. 리플로우한 후 130 $^{\circ}C$에서 열처리함에 따른 계면상 및 솔더 내부의 상변화를 관찰하였다. 계면에는 (Ni,Co)$_3$Sn$_4$외에 (Au,Ni,Co,Bi)Sn$_4$가 생성되었음을 관찰할 수 있었고, 솔더 내부에는 (Au,Ni,Co,Bi)SH$_4$, Ag$_3$Sn, Bi 상이 혼재되어 있었다. Nano-indentation에 의한 경도 측정 결과, Bi 함량 증가에 따라 경도는 증가하였으나, 볼전단(Ball Shear) 테스트 결과는 Bi가 증가됨에 따라 오히려 볼전단 강도값이 감소하였다. 이는 파면 검사 결과, 파괴 경로가 주로 계면의 금속간 화합물과 솔더 사이에서 진행함에 기인한 것이다. 솔더 내부의 파괴 경로를 가진 2.5Bi가 가장 우수한 볼전단 강도값을 나타내었는데, 이는 솔더내의 Bi의 고용강화에 기인한 것으로 보인다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.6
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• pp.481-486
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• 2010

ENIG (electroless Ni immersion gold) is one of surface finishing which has been most widely used in fine pitch SMT (surface mount technology) and BGA (ball grid array) packaging process. The reliability for package bondability is mainly affected by interfacial reaction between solder and surface finishing. Since the behavior of IMC (intermetallic compound), or the interfacial reaction between Ni and solder, affects to some product reliabilities such as solderability and bondability, understanding behavior of IMC should be important issue. Thus, we studied the properties of ENIG with P contents (9 wt% and 13 wt%), where the P contents is one of main factors in formation of IMC layer. The effect of P content was discussed using the results obtained from FE-SEM(field-emission scanning electron microscope), EPMA(electron probe micro analyzer), EDS(energy dispersive spectroscopy) and Dual-FIB(focused ion beam). Especially, we observed needle type irregular IMC layer with decreasing Ni contents under high P contents (13 wt%). Also, we found how IMC layer affects to bondability with forming continuous Kirkendall voids and thick P-rich layer.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.3
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• pp.27-33
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• 2008

With increasing use of portable appliances such as PDA and cellular phone, changing environment of applications requires higher solder joint reliability. The ENIG (Electroless Nickel Immersion Gold) process has been widely used for fine pitch SMT (Surface Mount Technology) and BGA (Ball Grid Array) packaged devices due to its benefits including excellent solderability, high uniformity and substantial legibility throughout the packaging process. Its brittle fracture of solder, however, has received increasingly attentions. It was Down that fracture brittleness is mainly related with black pad resulting from galvanic nickel corrosion and P-enriched layer formation between the IMC (Intermetallic Compounds) and electroless nickel layer. Theoretically, smooth electroless Ni layer was blown to have a advantages in minimizing the black pad phenomenon by uniform solution exchange during immersion gold plating. Nevertheless, how to control the surface morphology of electroless Ni layer has been hardly blown. This study investigates an effect of surface morphology of Cu underlayer on surface morphology of electroless Ni layer. To obtain various kinds of surface morphology of Cu layer, two types of Cu etching chemical and a number of Cu etching treatment were applied.