온도변화시험의 유지시간을 고려한 가속수명 시험법 개발

Abstract

반도체기술이 발전함에 따라 전자제품의 견박단소화 및 고성능화로 발전하고 있다. 부품이나 소재 등 크기가 매우 작아지고 있고 이에 따른 고장이 많이 일어나고 있어 신뢰성 향상을 위해 미국, 일본, 유럽, 한국 등 전 세계적으로 여러 분야에서 신뢰성 기술의 개발에 힘쓰고 있다. 또한, 신뢰성 해석, 신뢰도 예측 등을 높이기 위한 연구는 계속 진행되고 있고, 특히 최근 솔더 접합부에 고장이 많이 일어나고 있기 때문에 솔더 접합부 열화에 대하여 연구가 많이 진행되고 있다. 그 결과 열화에 미치는 주요인자는 기판과 솔더 접합계면의 금속화합물 (Inter-Metallic Compound, IMC)의 형성과 성장임이 밝혀졌다. 이 IMC는 고온와 온도변화에 의해 생성이 되고 열팽창 계수 차이에 의한 솔더 자체 크랙을 촉진시킨다. 따라서 IMC 형성에 의한 솔더 크랙 촉진을 확인하는 것과 피로수명을 보기위해 가속수명시험 중 온도변화시험을 실시한다. 시간에 따른 제품 구성 부품들에 솔더 접합부의 높은 신뢰도를 갖기 위해서는 수명평가가 중요하다. 일반적으로 수명평가에 있어 수명을 예측하는 데에는 가속수명시험 방법을 적용하며, 온도변화시험은 가속모형인 코핀-맨슨(Coffin-Manson) 모델을 사용한다. IMC 형성이 고온에서 일어나는 것으로 많이 알려져 있고 온도 변화 시험 설계 또한 온도변화, 고온노출을 적용하여 시험을 실시하지만 피로수명을 구하는 가속모델인 코핀-맨슨 모델에는 하나의 스트레스 조건인 온도차이만 적용이 되어 실제 시험조건인 고온노출, 즉 유지시간을 고려하지 않고 피로수명을 구하게 된다. 이에 본 연구에서는 온도변화시험의 유지시간을 고려한 가속수명시험법을 개발하였다. 기존 코핀-맨슨 모델은 온도차이만 고려하지만 유지시간이라는 시간 개념을 반영을 해야 되기 때문에 코핀-맨슨 모델을 변형을 할 필요성이 있다. 온도변화시험은 정의 구형파의 형태로 시험이 진행되고 두 가지 스트레스 조건을 가진 온도변화 시험은 양 구간을 고려한 정의 구형파(Bipolar aquare wave)형태로 시험이 진행된다. 따라서 양 구간을 고려한 정의 구형파의 수식을 코핀-맨슨 모델에 접목시키면 시간이 반영된 온도차이 값을 구할 수 있다. 기존 코핀-맨슨 모델과 제안한 코핀-맨슨 모델을 비교 분석한 결과 제안한 모형이 기존 모형보다 신뢰도가 더 높은걸 확인할 수 있었으며 제안한 방법으로 가속모델에 대한 신뢰성 향상에 기여할 수 있을 것으로 기대된다.|As technology of conductor is developing as well as electronics’s development of being light weight and short small with high performance. This development makes parts and materials to be smaller and cause more failure. In order to improve its reliability, world including USA, Japan, Europe and Korea widely are putting a lot of efforts into research about improving its reliability technology. Also to improve accuracy of reliability analysis and prediction, there are many ongoing researches. Especially soldering copula has been issues for many failures, research about soldering copula’s degradation has been in progress. In result, main influence factors for degradation are formation and growth of inter-metallic compound between printed circuit board and soldering copula become known. This IMC(inter-metallic compound) is usually formated by high temperature and sudden temperature change and its difference of coefficient of expansion often accelerated its cracks of soldering. Therefore Temperature change test during accelerated lifetime test is performed to check the acceleration of soldering cracks and fatigue life. To achieve high reliability for soldering copula of component parts as time passes by, it is important to do the lifetime test. In general, accelerated lifetime test is applied to predict its lifetime and coffin-Manson model has been used for time change test. Formation of IMC is occurred in the high temperature and plan of temperature change test also include change of temperature, exposure of high temperature and performed. But accelerated model, Cofffin-Manson model to calculate fatigue lifetime only by using difference of temperature as stress variables, and not including practical test condition such as high temperature exposure and dwell time. This thesis propose accelerate lifetime test including dwell time of temperature change test. General Coffin-Manson model only consider difference of temperature, so little modification required to Coffin-Manson model to apply dwell time concept. Change temperature test is performed as form of bipolar aquare wave which is change temperature test including two stress factors. Therefore apply equation of bipolar aquare wave into Coffin-Manson model, we can calculate the difference value of temperature which is influenced by time. We can confirm the proposed Conffin-Manson model has more reliable than general Coffin-Manson model by comparative analysis between two models and can improve the reliability of accelerated model by proposed model.; As technology of conductor is developing as well as electronics’s development of being light weight and short small with high performance. This development makes parts and materials to be smaller and cause more failure. In order to improve its reliability, world including USA, Japan, Europe and Korea widely are putting a lot of efforts into research about improving its reliability technology. Also to improve accuracy of reliability analysis and prediction, there are many ongoing researches. Especially soldering copula has been issues for many failures, research about soldering copula’s degradation has been in progress. In result, main influence factors for degradation are formation and growth of inter-metallic compound between printed circuit board and soldering copula become known. This IMC(inter-metallic compound) is usually formated by high temperature and sudden temperature change and its difference of coefficient of expansion often accelerated its cracks of soldering. Therefore Temperature change test during accelerated lifetime test is performed to check the acceleration of soldering cracks and fatigue life. To achieve high reliability for soldering copula of component parts as time passes by, it is important to do the lifetime test. In general, accelerated lifetime test is applied to predict its lifetime and coffin-Manson model has been used for time change test. Formation of IMC is occurred in the high temperature and plan of temperature change test also include change of temperature, exposure of high temperature and performed. But accelerated model, Cofffin-Manson model to calculate fatigue lifetime only by using difference of temperature as stress variables, and not including practical test condition such as high temperature exposure and dwell time. This thesis propose accelerate lifetime test including dwell time of temperature change test. General Coffin-Manson model only consider difference of temperature, so little modification required to Coffin-Manson model to apply dwell time concept. Change temperature test is performed as form of bipolar aquare wave which is change temperature test including two stress factors. Therefore apply equation of bipolar aquare wave into Coffin-Manson model, we can calculate the difference value of temperature which is influenced by time. We can confirm the proposed Conffin-Manson model has more reliable than general Coffin-Manson model by comparative analysis between two models and can improve the reliability of accelerated model by proposed model.