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Inference on Weibull percentiles from sudden death tests using maximum likelihood
412
WORLD
ABSTRACTS
ON
MICROELECTRONICS
t h e t e c h n i q u e s based on t h e m a x i m u m e n t r o p y principle lose m u c h of their appeal.
AND
RELIABII,ITY
censored testing. It is p r o p o s e d that this ratio be used as a criterion for d e t e r m i n i n g w h e t h e r a given s u d d e n death test is m o r e precise t h a n a given conventional test.
Inference on Weibull percentiles f r o m sudden death tests using m a x i m u m likelihood. J.I. M c C o o L . 1EEE Trans. Reliab. R-19, No. 4, N o v e m b e r
R a n d o m failure. D. BADENIUS. I E E E Trans. Rdhlb.
(1970), p. 177. A s u d d e n d e a t h test is a special case of a m u l t i p l y censored life test w h e r e i n an equal n u m b e r of r a n d o m l y selected s u r v i n g i t e m s are r e m o v e d f r o m t h e test following the occurrence of each failure. Confidence limits for t h e W e i b u l l - s h a p e p a r a m e t e r a n d a W e i b u l l percentile m a y be set with a s u d d e n d e a t h sample, u s i n g t h e m e t h o d of m a x i m u m likelihood. A n expression is f o u n d for t h e m e d i u m ratio of t h e u p p e r to lower 100 (1 ~) p e r cent confidence limits for a W e i b u l l percentile u n d e r either s u d d e n d e a t h or conventional type-I I
R-19, No. 3, A u g u s t (1970), p. 86. R a n d o m failure ~.~ p e r h a p s t h e m o s t a b u s e d t e r m in reliability and related e n g i n e e r i n g interests. Past definitions, being togicall) m o r e descriptive t h a n constructive, have not been truly definitive. A n a t t e m p t is m a d e here to offer one that is: t h e class of failures statistically i n d e p e n d e n t of past history. T h i s definition is based u p o n the m u t u a l implication b e t w e e n t h e stochastic processes p r o d u c i n g s u c h events a n d the u n i q u e characterization thereof bx their i n d e p e n d e n c e .
2. RELIABILITY O F C O M P O N E N T S , TUBES, T R A N S I S T O R S A N D ICs M i n i m i z a t i o n of misclassification of c o m p o n e n t failures in a two-component system. A. J. G a o s s . I E E E Trans. Reliab. R-19, No. 3, A u g u s t (1970), p. 120. In this p a p e r we a s s u m e we are repairing t w o - c o m p o n e n t series s y s t e m s that have failed or are m a l f u n c t i o n i n g . It is f u r t h e r a s s u m e d that w h e n a s y s t e m is b r o u g h t into the repair shop, it is n o t k n o w n with certainty w h i c h c o m p o n e n t has failed. If the r e p a i r m a n begins repairing t h e w r o n g c o m p o n e n t , a misclassification cost is incurred. It is also a s s u m e d that s o m e resources are available for t h e p u r c h a s e a n d operation of a failure detection m e c h a n i s m that, d e p e n d i n g on t h e a m o u n t allocated for detection, e n h a n c e s the probability of correctly detecting t h e failed c o m p o n e n t . A s t u d y is t h e n m a d e that is designed to m i n i m i z e t h e expected cost of failure detection. E x a m p l e s are included.
Acceleration factors for environmental testing of integrated circuits. E. S. ANOLICK, S. AMENDOLA a n d P. J. LEVlTZ. Proc. I E E E Reliab. Phys. Syrup., L a s Vegas, U . S . A . , 31 M a r c h - 2 April (1971). T h i s p a p e r discusses an e x p e r i m e n t to d e t e r m i n e acceleration factors for t e m p e r a t u r e a n d h u m i d i t y life testing based o n a single, p r i m a r y m o d e l of failure. T h e accelerating p a r a m e t e r s to be evaluated are t e m p e r a t u r e , h u m i d i t y , voltage a n d encapsulation. A m o d e l is p r e s e n t e d that explains t h e observed results a n d this r d a t e d to defect statistics.
Differential pressure test: A quantitative stress test m e t h o d for bonded b e a m - l e a d e d devices. E. J. BOORE a n d D. M . SUTTER. Proc. 21st Electronic Components Conf. W a s h i n g D.C., U . S . A . , 10-12 M a y (1971), p. 2. T h e differential p r e s s u r e test ( D P T ) is a m e t h o d developed for stress testing b o n d e d b e a m leaded devices. T h e test facility is basically a p n e u m a t i c p r e s s u r e c h a m b e r , c o n t a i n i n g t h e b e a m - l e a d e d chip with its associated substrate, a n d an e x h a u s t diffuser located directly over t h e chip w i t h provision for v a r y i n g t h e chip to diffuser spacing. T h e results of several test studies on chip arrays are presented. T h e s e results indicate t h e
D P T m e t h o d to be capable of detecting the full spcctr~;) of defects i n c l u d i n g : (1) individual h o n d defects; (2) metallizing defects on t h e s u b s t r a t e (adhesion); :rod (3 structural defects in t h e silicon chip. Comparison, s with visual inspection also s h o w that inspection is insutficicnt to assure structural integrity of b o n d e d chips. In general. visual inspection is s h o w n to result in u u w a r r a n t e d ]~s~ of p r o d u c t with serious b o n d i n g and chip defecta L*~im_, undetectable.
Design
limits w h e n using G o l d A I b o n d s . ~'. PHILOFSKY. Proc. I E E E Reliab. Phys. @,rap. Las Vega.~, U.S.A., 31 M a r c h - 2 April (1971). ( ; o l d - A l u m i n i u m wire b o n d s f o r m intermetallic p h a s e s with a n y elevated t e m p e r a t u r e t r e a t m e n t . Intermetallic formation alone does n o t cause b o n d failure. However, certain failure m o d e s - - o p e n metallization in t h e b o n d area, lifted wire b o n d s after aging, a n d heel breaks after t h e r m a l c y c l i n g - m a y be related to intermetallic formation. Specific causes of these failure m o d e s are discussed. T h e s e f o r m the basis for the r e c o m m e n d a t i o n s p r e s e n t e d as design limits w h e n u s i n g g o l d - a l u m i n u m wire b o n d s in circuits. Corrosion resistance of several integrated-circuit metallization systems. J. A. CUNNINGHAM, C. I~. FULLER a n d C. T . HAYWOOD. I E E E Trans. Reliab. R-19, No. 4, N o v e m b e r (1970), p. 182. Accelerated life data are p r e s e n t e d on several integrated-circuit metaI1lization s y s t e m i n c l u d i n g AI, M o - A u , T i - P t - A u and a n e w s y s t e m T i : ~V-Au w h e r e the R F s p u t t e r e d T i : W layer is a p s e u d o alloy of 10-20 per cent T i in W. Life tests include total water i m m e r s i o n , h i g h - p r e s s u r e s t e a m a n d 85°C/85 p e r cent R H bias on bare a n d plasticencapsulated devices. H e a t - a g e a n d resistivity-ratio data are p r e s e n t e d s h o w i n g t h e metallurgical stability of t h e T i : W - A u s y s t e m . T h e corrosion resistance decreases as T i - P t - A u 7> T i : W - A u >> M o - A u ~ AI.
Anticipatory test monitors IC suppliers process control. G. T H O ~ N ~ . Proc. I E E E Reliab. Phys. Symp. L a s Vegas, U . S . A . , 31 M a r c h - 2 April (1971). A test h a s
WORLD
ABSTRACTS
ON
MICROELECTRONICS
t h e t e c h n i q u e s based on t h e m a x i m u m e n t r o p y principle lose m u c h of their appeal.
AND
RELIABII,ITY
censored testing. It is p r o p o s e d that this ratio be used as a criterion for d e t e r m i n i n g w h e t h e r a given s u d d e n death test is m o r e precise t h a n a given conventional test.
Inference on Weibull percentiles f r o m sudden death tests using m a x i m u m likelihood. J.I. M c C o o L . 1EEE Trans. Reliab. R-19, No. 4, N o v e m b e r
R a n d o m failure. D. BADENIUS. I E E E Trans. Rdhlb.
(1970), p. 177. A s u d d e n d e a t h test is a special case of a m u l t i p l y censored life test w h e r e i n an equal n u m b e r of r a n d o m l y selected s u r v i n g i t e m s are r e m o v e d f r o m t h e test following the occurrence of each failure. Confidence limits for t h e W e i b u l l - s h a p e p a r a m e t e r a n d a W e i b u l l percentile m a y be set with a s u d d e n d e a t h sample, u s i n g t h e m e t h o d of m a x i m u m likelihood. A n expression is f o u n d for t h e m e d i u m ratio of t h e u p p e r to lower 100 (1 ~) p e r cent confidence limits for a W e i b u l l percentile u n d e r either s u d d e n d e a t h or conventional type-I I
R-19, No. 3, A u g u s t (1970), p. 86. R a n d o m failure ~.~ p e r h a p s t h e m o s t a b u s e d t e r m in reliability and related e n g i n e e r i n g interests. Past definitions, being togicall) m o r e descriptive t h a n constructive, have not been truly definitive. A n a t t e m p t is m a d e here to offer one that is: t h e class of failures statistically i n d e p e n d e n t of past history. T h i s definition is based u p o n the m u t u a l implication b e t w e e n t h e stochastic processes p r o d u c i n g s u c h events a n d the u n i q u e characterization thereof bx their i n d e p e n d e n c e .
2. RELIABILITY O F C O M P O N E N T S , TUBES, T R A N S I S T O R S A N D ICs M i n i m i z a t i o n of misclassification of c o m p o n e n t failures in a two-component system. A. J. G a o s s . I E E E Trans. Reliab. R-19, No. 3, A u g u s t (1970), p. 120. In this p a p e r we a s s u m e we are repairing t w o - c o m p o n e n t series s y s t e m s that have failed or are m a l f u n c t i o n i n g . It is f u r t h e r a s s u m e d that w h e n a s y s t e m is b r o u g h t into the repair shop, it is n o t k n o w n with certainty w h i c h c o m p o n e n t has failed. If the r e p a i r m a n begins repairing t h e w r o n g c o m p o n e n t , a misclassification cost is incurred. It is also a s s u m e d that s o m e resources are available for t h e p u r c h a s e a n d operation of a failure detection m e c h a n i s m that, d e p e n d i n g on t h e a m o u n t allocated for detection, e n h a n c e s the probability of correctly detecting t h e failed c o m p o n e n t . A s t u d y is t h e n m a d e that is designed to m i n i m i z e t h e expected cost of failure detection. E x a m p l e s are included.
Acceleration factors for environmental testing of integrated circuits. E. S. ANOLICK, S. AMENDOLA a n d P. J. LEVlTZ. Proc. I E E E Reliab. Phys. Syrup., L a s Vegas, U . S . A . , 31 M a r c h - 2 April (1971). T h i s p a p e r discusses an e x p e r i m e n t to d e t e r m i n e acceleration factors for t e m p e r a t u r e a n d h u m i d i t y life testing based o n a single, p r i m a r y m o d e l of failure. T h e accelerating p a r a m e t e r s to be evaluated are t e m p e r a t u r e , h u m i d i t y , voltage a n d encapsulation. A m o d e l is p r e s e n t e d that explains t h e observed results a n d this r d a t e d to defect statistics.
Differential pressure test: A quantitative stress test m e t h o d for bonded b e a m - l e a d e d devices. E. J. BOORE a n d D. M . SUTTER. Proc. 21st Electronic Components Conf. W a s h i n g D.C., U . S . A . , 10-12 M a y (1971), p. 2. T h e differential p r e s s u r e test ( D P T ) is a m e t h o d developed for stress testing b o n d e d b e a m leaded devices. T h e test facility is basically a p n e u m a t i c p r e s s u r e c h a m b e r , c o n t a i n i n g t h e b e a m - l e a d e d chip with its associated substrate, a n d an e x h a u s t diffuser located directly over t h e chip w i t h provision for v a r y i n g t h e chip to diffuser spacing. T h e results of several test studies on chip arrays are presented. T h e s e results indicate t h e
D P T m e t h o d to be capable of detecting the full spcctr~;) of defects i n c l u d i n g : (1) individual h o n d defects; (2) metallizing defects on t h e s u b s t r a t e (adhesion); :rod (3 structural defects in t h e silicon chip. Comparison, s with visual inspection also s h o w that inspection is insutficicnt to assure structural integrity of b o n d e d chips. In general. visual inspection is s h o w n to result in u u w a r r a n t e d ]~s~ of p r o d u c t with serious b o n d i n g and chip defecta L*~im_, undetectable.
Design
limits w h e n using G o l d A I b o n d s . ~'. PHILOFSKY. Proc. I E E E Reliab. Phys. @,rap. Las Vega.~, U.S.A., 31 M a r c h - 2 April (1971). ( ; o l d - A l u m i n i u m wire b o n d s f o r m intermetallic p h a s e s with a n y elevated t e m p e r a t u r e t r e a t m e n t . Intermetallic formation alone does n o t cause b o n d failure. However, certain failure m o d e s - - o p e n metallization in t h e b o n d area, lifted wire b o n d s after aging, a n d heel breaks after t h e r m a l c y c l i n g - m a y be related to intermetallic formation. Specific causes of these failure m o d e s are discussed. T h e s e f o r m the basis for the r e c o m m e n d a t i o n s p r e s e n t e d as design limits w h e n u s i n g g o l d - a l u m i n u m wire b o n d s in circuits. Corrosion resistance of several integrated-circuit metallization systems. J. A. CUNNINGHAM, C. I~. FULLER a n d C. T . HAYWOOD. I E E E Trans. Reliab. R-19, No. 4, N o v e m b e r (1970), p. 182. Accelerated life data are p r e s e n t e d on several integrated-circuit metaI1lization s y s t e m i n c l u d i n g AI, M o - A u , T i - P t - A u and a n e w s y s t e m T i : ~V-Au w h e r e the R F s p u t t e r e d T i : W layer is a p s e u d o alloy of 10-20 per cent T i in W. Life tests include total water i m m e r s i o n , h i g h - p r e s s u r e s t e a m a n d 85°C/85 p e r cent R H bias on bare a n d plasticencapsulated devices. H e a t - a g e a n d resistivity-ratio data are p r e s e n t e d s h o w i n g t h e metallurgical stability of t h e T i : W - A u s y s t e m . T h e corrosion resistance decreases as T i - P t - A u 7> T i : W - A u >> M o - A u ~ AI.
Anticipatory test monitors IC suppliers process control. G. T H O ~ N ~ . Proc. I E E E Reliab. Phys. Symp. L a s Vegas, U . S . A . , 31 M a r c h - 2 April (1971). A test h a s