Unitek UNIBOND 2, User Manual

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6.00. P R I N T E D _CIRCUIT WARD TRACE REPAIR
6.01. P a r a l l e l gap welding i s a s p e c i a l form o f s e r i e s welding i n which t h e s p a c -
ing, u s u a l l y l e s s t h a n 0 . 0 2 5 i n c h , between t h e e l e c t r o d e s i s such t h a t a s i n g l e weld
i s formed between t h e e l e c t r o d e s . T h e h e a t s i n k e f f e c t o f t h e e l e c t r o d e s u s u a l l y
l i m i t s f u s i o n t o approximately 80% o f t h e e l e c t r o d e gap.
In p a r a l l e l gap welding, F i g u r e s 2 2 ( a ) and ( b ) . t h e c u r r e n t d i s t r i b u t i o n between t h e
ribbon and s u b s t r a t e depends l a r g e l y o n t h e r e s i s t a n c e between t h e two conductors.
The contact r e s i s t a n c e v a r i e s w i t h t h e e l e c t r o d e f o r c e .
In a t y p i c a l r e p a i r. 2 2 ( c ) , t h e e l e c t r o d e s
should b e a s wide a s t h e r i b b o n .
An a l t e r n a t e e l e c t r o d e p o s i t i o n w i t h r e -
spect t o t h e Tr a c e i s shown i n 2 2 ( d ) . T h i s
technique i s sometimes used t o bond n a r -
row ribbon o r w i r e u s i n g a UNITIP.
6.02. G o l d - p l a t e d Kovar. u s u a l l y . 0 0 2 t o
.005 i n c h t h i c k , i s used t o r e p a i r gold o r
solder- p l a t e d boards which w i l l subsequent-
ly be ( a ) conformaly coated, o r ( b ) com-
pletely covered w i t h s o l d e r i n t h e r e p a i r e d
area, o r ( c ) n o t s u b j e c t t o high temper-
atures, h i g h humidity environments. G o l d
ribbon. . 0 0 2 i n c h t h i c k , i s t h e p r e f e r r e d
material f o r g o l d - p l a t e d o r unplated copper
traces. C o n f o r m a l c o a t i n g o f gold r i b b o n
repairs i s n o t r e q u i r e d .
6.03. T h e r e l i a b i l i t y and r e p e a t a b i l i t y
of welding gold p l a t e d Kovar i n t h e Vo l t a g e
Mode i s e x c e l l e n t . T h e s e t t i n g s i n Vo ltage
+ Current Mode a r e more c r i t i c a l , b u t t h e
number o f welds which can b e made b e f o r e
cleaning t h e e l e c t r o d e s w i l l b e increased.
DAMAGED TRACE
REPAIR RIB ON
MAW/Stv,i
(b)
SUBSTRATE
•
DIAGRAM OF TYPICAL REPAIR
Figure 2 2
(d)
6.04. C o p p e r w i r e , 2 9 t o 3 4 gauge, c a n be used t o make welded o r r e f l o w s o l d e r e d
repairs a n d / o r engineering changes o n unplated copper boards. U n p l a t e d , p l a t e d o r
tinned copper r i b b o n i s an i d e a l choice f o r r e f l o w soldered r e p a i r s b u t i s n o t recom-
mended f o r w e l d i n g because o f i t s l o w r e s i s t a n c e . S o m e users s u c c e s s f u l l y bond . 0 0 2
inch copper r i b b o n t o one ounce copper t r a c e s . T h i s process r e q u i r e s v e r y t i g h t p r o -
duction c o n t r o l s . C o p p e r w i r e a s l a r g e a s 20 gauge has been s u c c e s s f u l l y welded t o 1
oz b a r e copper t r a c e s u s i n g t h e Vo l t a g e + Current Feedback Mode o f t h e Unibond I I .
6.05. T h e width o f t h e r i b b o n should be approximately t h e same a s t h e t r a c e . F o r
boards w i t h l i n e w i d t h s and l i n e spacing g r e a t e r t h a n . 0 1 0 i n c h , a r i b b o n which i s
.002 t o . 0 0 5 i n c h narrower t h a n t h e t r a c e i s acceptable and makes alignment c o n s i d e r -
ably e a s i e r.
6.06. E U 1 0 0 1 o r EU2030M Molybdenum Electrodes, a r e used f o r welding gold o r copper.
EU1000, RWMA-2 E l e c t r o d e s , a r e used f o r welding g o l d - p l a t e d n i c k e l , Kovar o r o t h e r
high r e s i s t a n c e m a t e r i a l s . T h e e l e c t r o d e width i s u s u a l l y wider t h a n t h e r i b b o n .
Model PD P o l i s h i n g Disks a r e used t o keep t h e e l e c t r o d e s f l a t a n d c l e a n .
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