Unitek UNIBOND 2, User Manual

Page: 19 / 49

5.02. V A R I A B L E S FOR PARALLEL GAP WELDING
5 . 0 2 . 1 . G A P - The l a r g e r t h e distance between t h e e l e c t r o d e s . t h e Gap. t h e g r e a t e r
the energy r e q u i r e d t o make a given bond.
5 . 0 2 . 2 . F O R C E - I n c r e a s i n g t h e e l e c t r o d e f o r c e lowers t h e c o n t a c t r e s i s t a n c e between
the weldments and between t h e weldments and t h e e l e c t r o d e s . t h e r e f o r e . more energy i s
required t o make a g i v e n weld. T h e Force. i n most cases. should b e i n t h e knee o f t h e
Force v s Contact Resistance Curve. S e e F i g u r e 1 8 .
5.02.3. A R E A OF ELECTRODE FACE - The l a r g e r t h e e l e c t r o d e a r e a i n c o n t a c t w i t h t h e
weldments, t h e lower t h e pressure and t h e l a r g e r t h e s i z e o f t h e bond a r e a . A l a r g e r
face r e q u i r e s more energy provided t h e c o n t a c t resistan ces do n o t change d r a s t i c a l l y.
Lower pressure. f o r c e p e r u n i t o f a r e a , o n t h e weldments i s more l i k e l y t o cause s p i t -
ting o r s t i c k i n g . F o r conductive m a t e r i a l s . make t h a t p o r t i o n o f t h e e l e c t r o d e f a c e
which a c t u a l l y contacts t h e weldment a s s m a l l a s p r a c t i c a l .
5 . 0 2 . 4 . P U L S E DURATION - t h e l o n g e r t h e Pulse D u r a t i o n , t h e g r e a t e r t h e p e n e t r a t i o n
of t h e bond i n t o both weldments and t h e g r e a t e r t h e e f f e c t o f t h e h e a t upon t h e m e t a l -
l u r g i c a l s t r u c t u r e o f t h e weldments. I n g e n e r a l , u s e p u l s e d u r a t i o n s l e s s t h a n 15 ms
for bonding and d u r a t i o n s g r e a t e r t h a n 20 ms f o r b r a z i n g o r r e f l o w s o l d e r i n g . P u l s e
Duration i s c r i t i c a l , a n d should be k e p t t o a minimum, f o r conductive m a t e r i a l s . such
as copper. P u l s e D u r a t i o n i s a l s o c r i t i c a l when welding r e s i s t i v e m a t e r i a l s i n t h e
Voltage + Current Feedback Mode.
S e e Figures 17 a n d 1 9 .
5 . 0 2 . 5 . ELECTRODE MATERIALS - use RWMA 2 copper e l e c t r o d e s f o r r e s i s t i v e a n d / o r h a r d
materials such a s g o l d p l a t e d Kovar and nichrome. U s e molybdenum o r tungsten e l e c -
trodes f o r conductive o r s o f t m a t e r i a l s such a s copper and g o l d .
5.03. S e l e c t t h e a p p r o p r i a t e e l e c t r o d e s . P l a c e t h e Unibond i n t h e VOLTAGE Mode.
5.04. S t a r t i n g with a n AMPLITUDE o f
.5 v o l t and a DURATION o f 2 ms, system-
a t i c a l l y determine t h e appropriate com-
bination f o r s a t i s f a c t o r y bonds. F o r a
given AMPLITUDE. g r a d u a l l y increase t h e
DURATION u n t i l acceptable welds a r e made.
Increase t h e AMPLITUDE by . 2 V and r e p e a t
the process. T h i s method w i l l determine
the DURATION range r e q u i r e d t o make welds
for s e v e r a l values o f AMPLITUDE. T h e
Duration becomes more c r i t i c a l a s t h e
Amplitude i s increased. P l o t t h e values
obtained a s i l l u s t r a t e d t o t h e r i g h t :
Figure 13 i l l u s t r a t e s combinations o f
Pulse Amplitude, D u r a t i o n and Force s e t -
tings which r e s u l t i n acceptable bonding
of . 0 0 3 x . 0 1 5 g o l d p l a t e d Kovar r i b b o n
to an unplated . 0 1 5 i n c h wide. 1 o z c o p -
per t r a c e on a g l a s s epoxy p r i n t e d c i r -
c u i t board. M o d e l EU1000 Copper Unibond
Electrodes were used w i t h t h e Electrode
Gap s e t t o . 0 1 2 i n c h .
Ampl it ude
.9
.8
Poor Ve l do
.7 -
.6
.5
5 1 0 1 5 2 0
Duration (ms)
Figure 1 3