ACF를 이용한 CCM (Compact Camera Module)용 COF(Chip-On-Flex) 실장 기술 및 신뢰성 연구

정창규,백경욱,Chung, Chang-Kyu,Paik, Kyung-Wook 한국마이크로전자및패키징학회 2008 마이크로전자 및 패키징학회지 Vol.15 No.2

본 논문에서는 ACF를 이용한 CCM용 COF 어셈블리의 실장 기술을 연구하고 COF 어셈블리의 신뢰성 분석을 수행하였다. 열팽창계수, 모듈러스, 유리전이온도 등 경화 후 ACF의 열-기계적 물성들을 분석하였으며, ACF의 경화거동 결과를 바탕으로 COF 접합공정 온도 및 시간을 최적화하였으며, 도전입자의 변형 관찰 및 전기적 접촉 저항 측정을 통해 본딩 압력에 대한 최적화를 수행하였다. 또한 ACF 물질 특성이 COF어셈블리의 신뢰성에 미치는 영향을 알아보기 위해 열-싸이클 시험, 고온 유지 시험, 고온고습 시험을 수행하였다. 신뢰성 시험 수행 후 ACF를 이용한 COF 어셈블리의 신뢰성에 가장문제가 되고 있는 점은 열-싸이클 신뢰성 시험에서 나타난 ACF joint의 접촉 저항 증가 문제였고, 이는 ACF 자체의 열-기계적 물성과 밀접한 관계가 있음을 확인하였다. In this paper, the Chip-On-Flex (COF) assembly process using anisotropic conductive films (ACFs) was investigated and the reliability of COF assemblies using ACFs was evaluated. Thermo-mechanical properties of ACFs such as coefficient of thermal expansion (CTE), storage modulus (E'), and glass transition temperature $(T_g)$ were measured to investigate the effects of ACF material properties on the reliability of COF assemblies using ACFs. In addition, the bonding conditions for COF assemblies using ACFs such as time, temperature, and pressure were optimized. After the COF assemblies using ACFs were fabricated with optimized bonding conditions, reliability tests were then carried out. According to the reliability test results, COF assemblies using the ACF which had lower CTE and higher $T_g$ showed better thermal cycling reliability. Consequently, thermo-mechanical properties of ACFs, especially $T_g$, should be improved for high thermal cycling reliability of COF assemblies using ACFs for compact camera module (CCM) applications.

코인드 소더 범프의 수치해석

황태경(Tae-Kyung Hwang),나재웅(Jae-Woong Nah),백경욱(Kyung-Wook Paik),이순복(Soon-Bok Lee) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3

In this study, eutectic solder materials, Sn-37Pb, was tested and numerically analyzed for the solder bumps coining process. This process has an object that equal coined height could be achieved and the flatness of the coined surface should be guaranteed. Before the coining process was going on, the original solder bumps height is about 85 ㎛. To get the desired coined height, we must study about the effects of process variables such as process time(or coining rate), temperature, and etc. This eutectic solder material was developed to form an area-array type solder bumps and were tested under 4 coining rates and 4 process temperatures. To get the basis about experimental results, we performed numerical analyses considering the rate and temperature dependent material behaviors. These important factors of the coining process could be applied by adopting the published references. From the results of numerical analysis and experiment, as the process temperature increased, lower coining load were needed. And as the coining rate increased, higher coining load were need. But the effects of coining rate is less than that of temperature variation.

Ni/Au 및 OSP로 Finish 처리한 PCB 위에 스크린 프린트 방법으로 형성한 Sn-37Pb, Sn-3.5Ag 및 Sn-3.8Ag-0.7Cu 솔더 범프 계면 반응에 관한 연구

나재웅,손호영,백경욱,김원회,허기록,Nah, Hae-Woong,Son, Ho-Young,Paik, Kyung-Wook,Kim, Won-Hoe,Hur, Ki-Rok 한국재료학회 2002 한국재료학회지 Vol.12 No.9

In this study, three solders, Sn-37Pb, Sn-3.5Ag, and Sn-3.8Ag-0.7Cu were screen printed on both electroless Ni/Au and OSP metal finished micro-via PCBs (Printed Circuit Boards). The interfacial reaction between PCB metal pad finish materials and solder materials, and its effects on the solder bump joint mechanical reliability were investigated. The lead free solders formed a large amount of intermetallic compounds (IMC) than Sn-37Pb on both electroless Ni/Au and OSP (Organic Solderabilty Preservatives) finished PCBs during solder reflows because of the higher Sn content and higher reflow temperature. For OSP finish, scallop-like $Cu_{6}$ /$Sn_{5}$ and planar $Cu_3$Sn intermetallic compounds (IMC) were formed, and fracture occurred 100% within the solder regardless of reflow numbers and solder materials. Bump shear strength of lead free solders showed higher value than that of Sn-37Pb solder, because lead free solders are usually harder than eutectic Sn-37Pb solder. For Ni/Au finish, polygonal shaped $Ni_3$$Sn_4$ IMC and P-rich Ni layer were formed, and a brittle fracture at the Ni-Sn IMC layer or the interface between Ni-Sn intermetallic and P-rich Ni layer was observed after several reflows. Therefore, bump shear strength values of the Ni/Au finish are relatively lower than those of OSP finish. Especially, spalled IMCs at Sn-3.5Ag interface was observed after several reflow times. And, for the Sn-3.8Ag-0.7Cu solder case, the ternary Sn-Ni-Cu IMCs were observed. As a result, it was found that OSP finished PCB was a better choice for solders on PCB in terms of flip chip mechanical reliability.

Polyetherimide 접착제의 표면 처리에 따른 MCM-D 계면 접착력 및 고온고습 신뢰성 변화에 관한 연구

윤현국,고형수,백경욱,Yoon, Hyun-Gook,Ko, Hyoung-Soo,Paik, Kyung-Wook 한국재료학회 1999 한국재료학회지 Vol.9 No.12

Polyetherimide와 실리콘 사이의 RIE 처리 및 알루미늄 킬레이트 계열의 adhesion promoter 처리에 따른 접착력과 고온고습환경에서의 신뢰성 변화를 연구하였다. 실험 방법으로는 180$^{\circ}$ 필 테스트 및 <85$^{\circ}C$ 85%> 테스트, SEM, AFM, 증류수 접촉각 실험이 수행되었다. $^O_2$ RIE 실험 결과 초기 접착력은 RIE 처리시간에 따라 약간의 변화를 가져왔으나 고온고습 환경에서의 저항성은 급격히 떨어지는 것이 관찰되었고 이것은 표면 거칠기의 영향이 아닌 표면의 친수성 정도에 따른 것으로 나타났다. Al-chelate adhesion promoter의 경우 초기 접착력에는 변화가 없으나 고온 고습환경에서의 저항성이 크게 증가하였는데 이것은 표면이 소수성으로 변한 데 따른 것으로 나타났다. The adhesion strength and high temperature/high humidity reliability of polyetherimide (PEI) adhesive on silicon wafer after being treated by each reactive ion etching (RIE) Aluminum (Al)-chelate adhesion promoter were investigated. 180$^{\circ}$ peel test and <85$^{\circ}C$ 85%> humidity test were performed for the initial adhesion strength and high temperature/high humidity reliability, respectively. For investigating surface effect scanning electron microscope (SEM), atomic force microscope (AFM), deionized (DI)-water contact angle studies were carried out. To investigate RIE effect, PEI was treated with $^O_2$ RIE, and then laminated. The initial peel strength increased slightly from 1.6 kg/cm for the first 2 minutes, and then decreased. High temp/high humid resistance decreased rapidly by RIE etching. RIE treatment on PEI affected on both of roughness and hydrophilicity increase. Aluminum-chelate adhesion promoter was coated by spinning on silicon wafer. The initial peel strength showed no effect of adhesion promoter treatment, but high temp/high humidity resistance increased remarkably. Al-chelate adhesion promoter did not affect the roughness but increased hydrophilicity.

$BaTiO_3$ 입자 함량이 에폭시/$BaTiO_3$ 복합 내장형 커패시터 필름의 유전상수에 미치는 영향

조성동,이주연,현진걸,이상용,백경욱,Cho Sung-Dong,Lee Joo-Yeon,Hyun Jin-Gul,Lee Sang-Yong,Paik Kyung-Wook 한국마이크로전자및패키징학회 2004 마이크로전자 및 패키징학회지 Vol.11 No.2

[ $BaTiO_3$ ]분말의 양과 에폭시/$BaTiO_3$ 복합 내장형 커패시터 필름의 유전상수와의 관계를 살펴보고 이에 대해 고찰하였다. 이를 위해 $BaTiO_3$ 분말의 함량에 따른 에폭시/$BaTiO_3$ 복합 내장형 커패시터 필름의 밀도 변화와 필름의 표면 및 단면 모습을 관찰하였다. 또한 $BaTiO_3$ 분말의 함량을 높이기 위한 여러 가지 bimodal 조합에 따른 에폭시/$BaTiO_3$ 복합 내장형 커패시터 필름의 유전상수 변화를 관찰하였다. 단일 입자를 이용한 unimodal의 경우 유전상수가 가장 높게 측정된 $S_4$ 분말을 이용하여 얻을 수 있었던 유전상수의 최대값은 약 60 이었다. 최대값보다 과량의 $BaTiO_3$ 분말을 첨가하였을 경우, 에폭시/$BaTiO_3$ 복합 내장형 커패시터 필름의 유전상수가 감소하는데, 이는 과량의 분말을 수용하기 위해 생성된 기공에 의한 것이었다. Bimodal 조합의 경우 가장 큰 분말과 가장 작은 분말의 조합인 $S_5+C_1$ 조합이 $75\;vol\%$의 가장 많은 양의 분말을 넣어 가장 높은 유전상수 90 을 얻는데 성공하였다. We investigated the effect of $BaTiO_3$ powder content on the dielectric constant of epoxy/$BaTiO_3$ composite embedded capacitor films (ECFs). Variations of the dielectric constant of epoxy/$BaTiO_3$ composite ECFs with unimodal $BaTiO_3$ powder content were measured. To explain this result, density of the ECFs was measured, and surface and cross section images of the ECFs were observed. In addition, variations of the dielectric constant of epoxy/$BaTiO_3$ composite ECFs with various bimodal combinations were measured. In the case of unimodal powder, the maximum dielectric constant was about 60 at $60\;vol\%$ S4 powder. And more powder addition lowered the dielectric constant of the ECFs, which was due to voids or pores formation by excess $BaTiO_3$ powder. In the case of bimodal combination, $75vol\%\;BaTiO_3$ powder loading and the dielectric constant of 90 were achieved using $S_5+C_1$ combination, biggest and smallest powder combination.

다양한 조성의 Sn-Ag-Cu 합금계 무연 솔더볼과 ENIG(Electroless Ni Immersion Gold), Cu-OSP(Oraganic Solderability Preservertive) 금속 패드와의 계면 반응 연구

박용성,권용민,손호영,문정탁,정병욱,강경인,백경욱,Park, Yong-Sung,Kwon, Yong-Min,Son, Ho-Young,Moon, Jeong-Tak,Jeong, Byung-Wook,Kang, Kyung-In,Paik, Kyung-Wook 한국마이크로전자및패키징학회 2007 마이크로전자 및 패키징학회지 Vol.14 No.4

본 논문에서는 다양한 조성의 주석-은-구리 합금계 솔더볼과 ENIG 및 Cu-OSP 패드와의 계면 반응에 대해 연구하였다. ENIG 패드와 미량의 Sb이 첨가된 합금 솔더와의 계면 반응 시 다른 솔더에 비해 매우 얇은 100 nm 내외의 두께를 가진 P-rich Ni layer가 형성되었다. 미량의 Ni이 첨가된 합금 솔더와 Cu-OSP 금속 패드와의 계면 반응 시에는 다른 솔더와는 달리 균일한 두께의 $Cu_6Sn_5$ 금속간화합물이 형성되었으며 추가 리플로우 시에 금속간화합물 입자가 거의 성장하지 않았다. 또한 $150^{\circ}C$의 장시간 열처리 시에 다른 솔더에 비해 매우 얇은 두께의 $Cu_3Sn$ 금속간화합물이 형성되었다. In this study, we investigated the interfacial reactions between various Sn-Ag-Cu(SAC) solder alloys and ENIG(Electroless Ni Immersion Gold) and Cu-OSP(Organic Solderability Preservative) pad finish. In the case of the interfacial reaction between Sb added SAC solder and ENlf thinner P-rich Ni layer was formed at the interface. In the case of the interfacial reaction between Ni added SAC solder and Cu-OSP, the uniform $Cu_6Sn_5$, intermetallic compounds(IMCs) were formed and $Cu_6Sn_5$ grain did not grow after multiple reflows. Thinner $Cu_3Sn$ IMCs were farmed at the interface between $Cu_6Sn_5$ and Cu-OSP after $150^{\circ}C$ thermal aging.

간섭계를 이용한 고온 환경에서 플립 칩 전자 패키지의 신뢰성 평가

박진형(Jin-Hyoung Park),장경운(Kyung-Woon Jang),백경욱(Kyung-Wook Paik),이순복(Soon-Bok Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Flip-chip assemblies using an adhesive have been increasingly applied to PDA devices, mobile phones and LCD devices. The use of Adhesive flip chip type electronic package offers numerous advantages such as reduced thickness and a low process temperature. ACF (anisotropic conductive film) type packages for flip-chip packages are becoming more popular among producers due to the simple processing involved, as well as the direct contact between the bump and electrode. Despite numerous benefits, flip-chip type packages bare reliability problems. The most critical issue among them is their electrical performance deterioration upon consecutive thermal cycle damage and moisture absorption of the polymeric resin attributed to gradual delamination growth through chip and adhesive interface induced by CTE( coefficient of thermal expansion) mismatch driven shear and peel stresses. When the crack at a weak site of the electronic package occurs, thermal deformation of flip-chip package is changed.

미세피치용 Cu/SnAg 더블 범프 플립칩 어셈블리의 신뢰성에 관한 연구

손호영,김일호,이순복,정기조,박병진,백경욱,Son, Ho-Young,Kim, Il-Ho,Lee, Soon-Bok,Jung, Gi-Jo,Park, Byung-Jin,Paik, Kyung-Wook 한국마이크로전자및패키징학회 2008 마이크로전자 및 패키징학회지 Vol.15 No.2

본 논문에서는 유기 기판 위에 $100{\mu}m$ 피치를 갖는 플립칩 구조인 Cu(60 um)/SnAg(20 um) 더블 범프 플립칩 어셈블리를 구현하여 이의 리플로우, 고온 유지 신뢰성, 열주기 신뢰성, Electromigration 신뢰성을 평가하였다. 먼저, 리플로우의 경우 횟수와 온도에 상관없이 범프 접속 저항의 변화는 거의 나타나지 않음을 알 수 있었다. 125도 고온 유지 시험에서는 2000시간까지 접속 저항 변화가 관찰되지 않았던 반면, 150도에서는 Kirkendall void의 형성으로 인한 접속 저항의 증가가 관찰되었다 또한 Electromigration 시험에서는 600시간까지 불량이 발생하지 않았는데 이는 Al금속 배선에서 유발되는 높은 전류 밀도가 Cu 칼럼의 높은 두께로 인해 솔더 영역에서는 낮아지기 때문으로 해석되었다. 열주기 시험의 경우, 400 cycle 이후부터 접속 저항의 증가가 발견되었으며, 이는 열주기 시험 동안 실리콘 칩과 Cu 칼럼 사이에 작용하는 압축 변형에 의해 그 사이에 있는 Al 및 Ti 층이 바깥쪽으로 밀려나감으로 인해 발생하는 것으로 확인되었다. In this study, reliabilities of Cu (60 um)/SnAg (20 um) double-bump flip chip assemblies were investigated for the flip chip interconnections on organic substrates with 100 um pitch. After multiple reflows at $250^{\circ}C\;and\;280^{\circ}C$, bump contact resistances were almost same regardless of number of reflows and reflow temperature. In the high temperature storage test, there was no bump contact resistance change at $125^{\circ}C$ up to 2000 hours. However, bump contact resistances slightly increased at $150^{\circ}C$ due to Kirkendall voids formation. In the electromigration test, Cu/SnAg double-bump flip chip assemblies showed no electromigration until about 600 hours due to reduced local current density. Finally, in the thermal cycling test, thermal cycling failure mainly occurred at Si chip/Cu column interface which was found out the highest stress concentration site in the finite element analysis. As a result, Al pad was displaced out under thermal cycling. This failure mode was caused by normal compressive strain acting Cu column bumps along perpendicular direction of a Si chip.

레이저 간섭계 ( ESPI ) 를 이용한 폴립칩 패키지의 열변형 평가

장우순(Woo Soon Jang),이백우(Baik Woo Lee),김동원(Dong Won Kim),정증현(Jeung Hyun Jeong),백경욱(Kyung Wook Paik),권동일(Dong Il Kwon),나전웅(Jae Woong Nah) 대한금속재료학회 ( 구 대한금속학회 ) 2002 대한금속·재료학회지 Vol.40 No.9

In this study, electronic speckle pattern interferometry (ESPI) was applied to a non-destructive and real-time evaluation of the thermal deformation in a flip-chip package. The displacement resolution of ESPI was improved with magnifying lenses, and ESPI was modified to measure the deformation of micro systems. The flip-chip package thermally deforms with increasing temperature, and the difference in the thermal expansion between the chip and the PCB induces the micro-failure at the solder joint. To evaluate the level of thermal deformation precisely, the horizontal and vertical deformations were measured in the temperature range of 25℃ to 125℃ in situ using the resolution-enhanced ESPI to a sub-micrometer scale. From the experimental results, it was found that the CTE (coefficient of thermal expansion) difference between the chip and the PCB leads to shear strain at the solder joint. In addition, the shear strain could be evaluated at each solder joint. To verify these experimental results, the finite element analysis(FEA) results were compared with the ESPI results. The FEA results were similar to the ESPI results, which confirmed the adequacy of our application.

레이저 간섭계(ESPI)에 의해 측정된 플립칩 열변형의 유한요소해석 모델링을 통한 솔더볼의 유동곡선 평가

이백우,김주영,나재웅,백경욱,권동일 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.6

The goal of this study was to determine the uniaxial flow curve for solder balls in a flip-chip from experimental-computational algorithms based on finite element modeling (FEM) of in-plane thermal displacement data measured by electronic speckle pattern interferometry (ESPI). In order to measure the deformation of such tiny components as the solder balls in the flip-chip, the spatial resolution of ESPI was increased to submicron scale by magnifying the areas studied. The flow curve for solder balls in the flip-chip was determined by the algorithm, which effectively matches the simulated solder deformation by FEM to the measured deformation by ESPI. The algorithms were applied to Sn-36Pb-2Ag flip-chip solder balls. The flow curve obtained for flip-chip solder was compared with those for bulk solder. The microstructure was also studied to clarify the flow curve results.