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Reliability of metal/glass-ceramic junctions made by solid state bonding
G. Lascar, Daniel Broussaud, Alain Thorel, Georges Cailletaud, J. Roland
To cite this version:
G. Lascar, Daniel Broussaud, Alain Thorel, Georges Cailletaud, J. Roland. Reliability of metal/glass-
ceramic junctions made by solid state bonding. Journal de Physique Colloques, 1986, 47 (C1), pp.C1-
139-C1-145. �10.1051/jphyscol:1986120�. �jpa-00225548�
JOURNAL DE PHYSIQUE
Colloque C1, suppl6ment au n02, Tome 47, f b v r i e r 1986 page cl-139
RELIABILITY OF METAL/GLASS-CERAMIC JUNCTIONS MADE BY SOLID STATE BONDING
G. LASCAR, D. BROUSSAUD*, A. THOREL*, G. CAILLETAUD' and J.J. ROLAND
QUANTEL, 17 Avenue d e l l A t l a n t i q u e , F-91402 O r s a y , France 'centre d e s M a t e r i a u x d e 1 ' E c o l e d e s Mines d e Paris, B . P . 8 7 ,
F-91003 E v r y C e d e x , France
Resume - L ' a s s e m b l a g e p a r d i f f u s i . o n d i t p a r thermo-compressi on permet d e
-- r e a l i s e r d e s l i a i s o n s ceramique-metal e t a n c h e s
.?l ' h e l i u m . Ce procBd6 engendre
ic e p e n d a n t d e s c o n t r a i r ~ t e s r 6 s i d u e l l e s d ' o r i g i n e ther'rnique s o u s l ' a c t i o n d e s q u e l l e s l e s d 6 f a u t s de l a ceramique p e u v e n t s e p r o p a g e r e t c o n d u i r e 5 l a r u p t u r e d i f f e r & d e 1 ' a s s e m b l a g e . Ce phBnomkne e s t m i s e n e v i d e n c e s u r d e s a s s e m b l a g e s v i t r o c ~ r a m i q u e / A l / I n v a r oC une m e i l l e u r e f i a b i l i t 6 e s t a s s u r 6 e p a r une r e d u c t i o n d e s d e f a u t s de s u r f a c e .
A b s t r a c t - The s o l i d s t a t e d i f f u s i o n bonding l e a d s t o h e l i u m - t i g h t ceramic- m e t a l j u n c t j . o n s . However t h i s t e c h n i q u e i n d u c e s r e s i d u a l s t r e s s e s due t o e x p a n s i o n mismatches which may c a u s e c e r a m i c f l a w s t o p r o p a g a t e h e n c e j u n c t i o n d e l a y e d f a i l u r e . T h i s phenomenon i s e v i d e n c e d on g l a s s - c e r a m i c / A l / I n v a r j u n c t i o n s from which a b e t t e r r e l i a b i l i t y i s e n s u r e d by a r e d u c t i o n o f s u r f a c e f l a w s .
I - INTRODUCTION
The f a b r i c a t i o n o f e l e c t r o - o p t i c a l components o f kii.gh q u a l i t y and r e l i a b i l i t y l e a d u s t o a c h i e v e metal-cerami c j u n c t i o n s by s o l i d s t a t e d i f f u s i o n bonding. The d i m e n s i o n a l s t a b i l i t y r e q u i r e d f o r s u c h components d i c t a t e d t h e s e l e c t i o n o f n e a r - t o - z e r o t h e r m a l e x p a n s i o n c o e f f i c i e n t s f o r t h e m a t e r i a l s t o b e j o i n e d namely a g l a s s - c e r a m i c and a f e r r o - n i c k e l a l l o y . The j u n c t i o n i s e x p e c t e d t o be h e l i u m - t i g h t and t o remain s o a f t e r 20 000 h o u r s ' o p e r a t i o n i n a d d i t i o n i t s h o u l d h o l d t e m p e r a t u r e up t o 200°C and r e s i s t s t h e r m a l shock from t h i s p o i n t down t o -50°C. I n o r d e r n o t t o a f f e c t t h e g l a s s - c e r a m i c p r o p e r t i e s t h e j o i n i n g p r o c e s s t e m p e r a t u r e s h o u l d n o t exceed t h e t r a n s i t i o n p o i n t shown t o be around 82O0C, t h e r e f o r e t e c h n i q u e s s u c h a s b r a z i n g o r g l a s s s o l d e r i n g a r e t o be a v o i d e d .
S o l j d s t a t e d i f f u s i o n bonding u s i n g aluminjum a s i n t e r m e d i a t e m a t e r i a 1 h a s been proved i n t h e p a s t t o be v e r y e f f i c i e n t i n t h e j o i n i n g o f g l a s s , s a p p h i r e o r alumina t o m e t a l / I / , / 2 / . T h i s t e c h n i q u e was l a t e l y e x t e n d e d t o non-oxide c e r a m i c s and shown t o a l l o w h e a t and t h e r m a l shock r e s i s t a n t j u n c t i o n s / 3 / . h'owever t h e h i g h ther'rnal e x p a n s i o n o f aluminium and o f m e t a l s r e l a t i v e l y t o c e r a m i c s i s e x p e c t e d t o y i e l d r e s i d u a l s t r e s s e s t h a t may c a u s e c a t a s t r o p h i c f a j l u r e a f t e r c o o l i n g o r a f t e r t h e r m a l c y c l i n g .
The p r e s e n t s t u d y was u n d e r t a k e n a f t e r t h e o b s e r v a t ~ o n o f d e l a y e d f a l l u r e s o f g l a s s - c e r a m l c / m e t a l j u n c t l o n s
W It h o u t a p p l l c a t l on o f add1
tlo n a l s t r e s s . I t a1 m s a t t h e d ~ t e r m l n a t i o n o f t h e s t r e s s f l e l d t h e r m a l l y i n d u c e d a f t e r t h e
joiningp r o c e s s and t h e n a l l o w l n g f o r t h e s e n s l t ~ v l t y t o slow c r a c k growth o f t h ? g l a s s - cerarnlc t h e s u r f a c e d e f e c t s were s u s p e c t e d t o p l a y a major r o l e on t h e ~ u n c t ~ o n r e l l a b l l l t y .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986120
CI-140 J O U R N A L DE PHYSIQUE
I1 - EXPEKIMENTAL
1. J o i n i n g t e c h n i q u e . The s o l i d s t a t e d i f f u s i o n bonding c o n s i s t s i n i n t e r p o s i n g a m e t a l g a s k e t between t h e c e r a m i c and m e t a l s u r f a c e s t o b e bound. The s a i d g a s k e t i s t h e n p l a s t i c a l l y deformed by r a p i d l y s q u e e z i n g t h e assembly a t a t e m p e r a t u r e r a n g i n g from 0 . 5 t o 0.9'Tm (Tm = m e l t i n g p o i n t o f t h e i n t e r m e d i a t e m e t a l ) . The b o n d i n g i s due t o v a r i o u s i n t e r f a c e r e a c t i o n s d e p e n d i n g upon t h e m a t e r i a l s and t h e j o i n i n g p a r a m e t e r s .
I n o u r c a s e a low e x p a n s i o n g l a s s - c e r a m i c ( a
2~ o - ~ . o c - ~ ) was s e a l e d t o i n v a r - t y p e f e r r o n i c k e l a l l o y u s i n g a n aluminium r i n g o f h e x a g o n a l c r o s s s e c t i o n . The s u r f a c e s t o be i n c o n t a c t were ground f l a t up t o a p o l i s h a c c e p t a b l e f o r h e l i u m - t i g h t n e s s and c l e a n e d . P r i o r t o j o i n i n g t h e components x e r e t h e r m a l l y t r e a t e d i n o r d e r t o r e l a x t h e r e s i d u a l s t r e s s e s and t o g e t some p r i m a r y r e c r y s t a l l i z a t i o n . The bonding a c h j eved a t a b o u t 50OoC i n f l o w i n g n i t r o g e n added w i t h 1 0 7 h y d r &en, -P
under a compressi v r l o a d r a n g i n g from 20 t o 6 0 W a . The s t r a i n r a t e ( - lo-' m . s ) i s h i g h enough t o b r e a k t h e s u r f a c e alumina on t h e r i n g . Bonding t h e n o c c u r s between f r e s h alumi n j um and t h e g l a s s - c e r a m i c v i a o x i d o - r e d u c t i on and f r i c t i o n a d h e s i o n p r o c e s s e s on one s i d e and between aluminium and m e t a l v i a d i f f u s i o n o n t h e o t h e r s i d e . T h e r e might b e some d i f f u s i o n between aluminium and t h e g l a s s - c e r a m i c b u t i t i s h a r d l y d e t e c t a b l e by c o n v e n t i o n a l mi c r o p r o b e a n a l y s i s . I n comparable e x p e r i m e n t s c o n d u c t e d e l s e w h e r e / 4 / some d i f f u s i o n Nas o u t l i n e d on a v e r y s h o r t r a n g e v i a SIXS a n a l y s i s . T h i s i n t e r f a c e r e a c t i o h a s p e c t i s u n d e r f u r t h e r i n v e s t i g a t i o n and wi 11 be d i s c u s s e d e l s e w h e r e .
The s c h e m a t i c o f t h e t e c h n i q u e i s shown o n F i g . 1, t h e d e t a i l s o f t h e p r o c e s s have been p r e s e n t e d e l s e w h e r e / 5 / , t h e a s p e c t r a t i o o f t h e aluminium r i n g was v a r i e d from 1 t o = 20 by t h e d e f o r m a t i o n p r o c e s s - and a n e l e c t r o - o p t i c a l assembly t h u s made i s a l s o shown /6/.
20 to 60 MPa
F i g . 1 - Schematic o f t h e bonding t e c h n i q u e and view o f a n e l e c t r o - o p t i c a l assembly.
2. R e l i a b i l i t y o f t h e j u n c t i o n . I t h a s been o b s e r v e d t h a t from a p o p u l a t i o n o f 40 j u n c t i o n s a c h i e v e d accordi.ng t o t h e same bonding p r o c e d u r e 7 o f t h o s e p e r i s h e d by d e l a y e d f r a c t u r e o f t h e g l a s s - c e r a m i c a f t e r d i f f e r e n t p e r i o d s o f t i m e - from 1 t o 600 h o u r s - though a l l 40 were f o u n d t o b e h e l i u m - t i g h t a f t e r j o i n i n g . The r e m a r k a b l e f a c t i s t h a t a l l t h o s e 7 were o b t a i n e d from g l a s s - c e r a m i c p a r t s t h e s u r f a c e s o f which had been o n l y ground whereas a l l p o l i s h e d s u r f a c e s y i e l d e d j u n c t i o n s w i t h l i f e t i m e s o v e r 1 0 000 h o u r s . T a b l e I summarizes t h o s e o b s e r v a t i o n s , a l l s u r v i v o r s c o u l d r e s i s t t h e 200°C t h e r m a l shock t e s t .
Zerodur from s c h o t t : 70 t o 75 w t % 6 e ~ ~ ~ r v n t i t e and g l a s s f o r b a l a n c e .
I I I I
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b e f e c t maximum Number o fI
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T a b l e I - J u n c t i o n s l i f e t i m e s o b s e r v e d a f t e r bonding v s s u r f a c e p r e p a r a t i o n
S t a r t i n g from t h e s e c o n s i d e r a t i o n s we came up w i t h t h e i d e a t h a t d e l a y e d f r a c t u r e c o u l d p e r t a i n t o some c r a c k growth phenomenon - a s p r e v i o u s l y o b s e r v e d f o r soda- l i m e - s i l i c a g l a s s e s i n m o i s t u r e - c o n t a i n i n g atmosphere /7/ c o n n e c t e d w i t h t h e p r e s e n c e o f d e f e c t s r e s u l t i n g from t h e s u r f a c e f i n i s h o f t h e g l a s s - c e r a m i c . The o b s e r v a t i o n o f a f r a c t u r e d specimen s u c h a s shown i n F i g . 2
js c o n s i s t e n t w i t h t h i s i d e a , it c a n b e s e e n t h a n t h e f r a c t u r e i n i t i a t e d from t h e s u r f a c e and p r o p a g a t e d i n t h e body d e v i a t i n g towards t h e c e n t e r h o l e o f t h e specimen by c o n t o u r i n g t h e zone u n d e r l y i n g t h e i n t e r f a c e .
qlass \ -- ceiamic
F i g . 2 - F r a c t o g r a p h y o f t h e g l a s s - c e r a m i c and c r o s s s e c t i o n of t h e f r a c t u r e d m e t a l / g l a s s - c e r a m i c j u n c t i o n .
S i n c e no a d d i t i o n n a l s t r e s s e s have been a p p l i e d o n t o t h e specimens a f t e r j o i n i n g one s h o u l d s u s p e c t r e s i d u a l s t r e s s e s r e s u l t i n g from t h e p r o c e s s t o b e r e s p o n s i b l e f o r t h e c r a c k p r o p a g a t i o n i n t h e g l a s s - c e r a m i c .
3. Mechanical c a r a c t e r i z a t i o n o f t h e g l a s s - c e r a m i c . S i n c e t h e above-mentionned
s t r e s s e s a r e e x p e c t e d t o b e complex, d i f f e r e n t t e s t i n g t e c h n i q u e s have been used t o
d e t e r m i n e t h e f a i l u r e s t r e s s o f t h e g l a s s - c e r a m i c . T a b l e I1 g i v e s t h e v a l u e s o b t a i n e d
v s t h e t e s t j n g mode and comparable r e s u l t s a l l o w i n g f o r t h e s u r f a c e f i n i s h a r e a l s o
g i v e n . I t i s t o be n o t e d t h a t t h e s t r e n g t h l e v e l i s reduced by a f a c t o r o f 2 when t h e
s u r f a c e i s a s ground i n s t e a d o f p o l i s h e d . O p t i c a l microscopy r e v e a l e d d e f e c t s of up
t o 30 pm and 10 wm i n s i z e r e s p e c t i v e l y , which i s c o n s i s t e n t w i t h t h e d i f f e r e n c e o f
s t r e n g t h l e v e l .
JOURNAL DE PHYSIQUE
i Testing mode 1 Surface preparation i Failure stress i Weibull i
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Table I1 - S t r e n g t h c h a r a c t e r i s t i c s o f t h e g l a s s - c e r a m i c v s s u r f a c e p r e p a r a t i o n . The c r i t i c a l s t r e s s i n t e n s i t y f a c t o r KIC h a s been d e t e r m i n e d u s i n g t h r e e t e c h n i q u e s , V i c k e r s i n d e n t a t i o n - d i r e c t / 8 / and p o s t f l e x u r e s t r e n g t h / 9 / - and d o u b l e t o r s i o n
/ l o / , v a l u e s between 0 , 6 and 1 , 1 5 MPa.fiwere o b t a i n e d .
The s e n s i t i v i t y t o slow c r a c k growth h a s been i n v e s t i g a t e d u s i n g t h e d o u b l e t o r s i o n t e c h n i q u e / 7 / , / 1 0 / w i t h 8 0 x 40 x 5 mm3 p l a t e s ( F i g . 3 ) i n atmospheres c o n t a i n i n g from 1 6 % t o 100 %,humidity. D i r e c t v i s u a l i z a t i o n o f c r a c k e x t e n s i o n was performed.
R e s u l t i n g V = A KI c u r v e s t h a t e x p r e s s e s t h e c r a c k p r o p a g a t i o n r a t e da v s s t r e s s
A+
-"
i n t e n s i t y f a c t o r K- d e r i v e d from-the formula : ,
I
K = P W [
I w d dn
where P i s t h e a p p l i e d l o a d and
-- v t h e P o i s s o n r a t i o ( s e e F i g . 3 f o r t h e o t h e r t e r m s ) a r e a l s o p r e s e n t e d .
F i g 3 - Double t o r s i o n specimen used f o r t h e d e t e r m i n a t i o n o f KI and KI ( V ) c u r v e s o b t a i n e d i n v a r i o u s m o l s t u r e - c o n t a i n i n g e n v i r o n m e n t s .
A and n v a l u e s were c a l c u l a t e d by l i n e a r r e g r e s s i o n and found t o be 0 , 7 1 and 1 6 , 8 r e s p e c t i v e l y , t h e s e p a r a m e t e r s t h u s c h a r a c t e r i z e t h e s e n s i t i v i t y o f t h e c o n s i d e r e d g l a s s - c e r a m i c i n a m o i s t u r e c o n t a j n i n g environment. Wether t h e l a t t e r is s a t u r e d o r n o t d o e s n o t a f f e c t t o a g r e a t e x t e n t t h e c r a c k p r o p a g a t i o n r a t e , t h i s i s c o n s i s t e n t w i t h t h e f a c t t h a t t h e c h e m i c a l p o t e n t i a l a t t h e c r a c k t i p i s r a t h e r c o n s t a n t whatever t h e o v e r a l l OH-concentration.
A t t h i s s t a g e i t i s p o s s i b l e t o p r e d i c t t h e l i f e t i m e o f t h e j u n c t i o n u s i n g t h e Weibull d i s t r i b u t i o n p a r a m e t e r s ( s e e T a b l e 11); i n t h e formalism d e r i v e d from G r i f f i t h ' s Law.
& T
3CI'vl 2''.-:--.= - - '?
'12
KI-P W ~ [ ~ I '
p / ~ UPPER SURFACE
-
- Humidity
:lo-6
- 1 0 8 -0.7
-0.6 6.5 -0.4 -0.3 1 -0.2
I I I I I
LOG
KIThus Time t o F a i l u r e ( t ) v s P r o b a b i l i t y o f r u p t u r e a t c o n s t a n t a p p l i e d s t r e s s (0,) c a n be e x p r e s s e d a s f o l l o w :
2 oon-2 I n - 1 n-2
t = 1-P ] m
onn. Ah-2)KIC n-2 [s m+ 1
where m and o a r e t h e Weibull p a r a m e t e r s , A and n t h e c r a c k growth p a r a m e t e r s and P t h e probabi l i & o f r u p t u r e .
-6 2 T a k i n g m = 7 , 8 , o = 4 3 , 4 A = 0 , 7 1 n = 1 6 , 8 K I C = 0 , 6 1 ~ p a . & S = 2 4 0 . 1 0 m a l l o w t o p l o t S t r e n g t h - P r o b a b i l i t y - T i m e (SPT) d i a g r a m s a s shown on F i g . 4. which p e r t a i n t o p o l i s h e d g l a s s - c e r a m i c specimens. They show f o r example t h a t under a t e n s i l e s t r e s g o f 40 MPa t h e g l a s s - c e r a m i c h a s 1 0 % f a i l u r e p r o b a b i l i t y a f t e r 1000 h o u r s
(14.10 s ) .
The knowledge o f t h e s t r e s s l e v e l and d i r e c t i o n t h e n a p p e a r e d o f prime i m p o r t a n c e t o a s s e s s t h e r e l i a b i l i t y o f t h e j u n c t i o n .
111 - STUDY OF THE RESIDUAL STRESS FIELD AFTER JOINING
The f i r s t approach c o n s i s t e d i n c o n s i d e r i n g t h e Evans' r e l a t i o n s h i p a p p l i e d f o r t h e r m a l e l a s t i c s t r e s s e s i n a body s u b m i t t e d t o a t h e r m a l shock :
E a A T
o = -
1- v
Strength
(MPa)F i g . 4 - SPT diagrams f o r t h e g l a s s - c e r a m i c .
I t can be shown t h a t t h e r m a l s t r e s s e s i n d u c e d by t h e e x p a n s i o n mismatch a f t e r bonding i n t h e j o i n e d assembly may be e x p r e s s e d a s f o l l o w / 5 / .
where E = Young's modulus
o f t h e metal a = mean e x p a n s i o n c o e f .
e = t h i c k n e s s and h = c o n t a c t w i d t h
AT = T p r o c e s s - T r e f e r e n c e
K = geometry f a c t o r bound t o t h e m e t a l s u b s t r a t e thickness.
T h i s a n a l y t i c a l f o r m u l a a l l o w s t h e c a l c u l a t i o n of t h e maximum s t r e s s t h e r m a l l y i n d u c e d
a t t h e i n t e r f a c e . Depending upon t h e t h i c k n e s s o f t h e m e t a l s u b s t r a t e - from 0 . 5 mm
t o 1 mm - t h a t a f f e c t s t h e v a l u e o f K , we h a v e c a l c u l a t e d strpss v a l u e s r a n g i n g from
50 t o 1 6 0 MPa ( t h e t h i c k e r t h e m e t a l t h e h i g h e r t h e s t r e s s ) . Though t h i s approach
JOURNAL DE PHYSIQUE
g i v e s some i d e a o f t h e s t r e s s l e v e l i t d o e s n ' t g i v e any i n d i c a t i o n on b o t h t h e d i s t r i b u t i o n and t h e d i r e c t i o n o f s t r e s s e s and d o e s n ' t t a k e a c c o u n t o f t h e b e h a v i o u r o f t h e i n t e r m e d i a t e aluminium l a y e r - which seems more c r i t i c a l f o r i n some c a s e s t h e c a l c u l a t e d s t r e s s i s o v e r t h e y i e l d s t r e s s o f t h e m e t a l i t s e l f .
F i n i t e e l e m e n t a n a l y s i s was t h e n c a r r i e d o u t f o r f u r t h e r r e f i n e m e n t o f s t r e s s e s e v a l u a t i o n u s i n g t h e v a l u e s o f E , v a n d a shown i n T a b l e I11 f o r t h e t h r e e components t o be bound. The a n a l y s i s was done f o r b i d i m e n s i o n a l and a x i s y m e t r i c a l modes, w i t h l i n e a r d i s p l a c e m e n t . The l i m i t c o n d i t i o n s were t a k e n a s f o l l o w :
- e l a s t i c b e h a v i o u r f o r m e t a l and c e r a m i c s u b s t r a t e s w i t h no t e m p e r a t u r e dependence.
- a l l o w a n c e was made f o r t h e p l a s t i c b e h a v i o u r o f aluminium, c o n s i d e r e d a s i s o t r o p i c and non t e m p e r a t u r e - d e p e n d e n t .
- t h e s t r e s s i s p u r e t h e r m a l w i t h AT = 50OoC.
The b a s i c mesh c o r r e s p o n d i n g t o t h e a c t u a l e l e c t r o - o p t i c a l component i s shown on Fi.g. 5 a l o n g w i t h t h e r e s u l t i n g i s o s t r e s s l i n e s . The s t r e s s a n a l y s i s t h e n showns t h a t normal s t r e s s e s a r e found n e a r t h e o u t e r c y l i n d r i c a l s u r f a c e o f t h e g l a s s - c e r a m i c s u b s t r a t e whereas c o m p r e s s i v e s t r e s s e s a r e o u t l i n e d a r o u n d t h e c e n t r a l b o r e .
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