Development Of "The Maple Method"

Abstract

1 . I N T R O D U C T I O N Recently TAB(Tape Automated Bonding)has become t h e main d r i v e r I C Assembly method f o r LCD(Liquid Crystal Disp1ay)modules. The reasons f o r t h e f i n e r p i tches a r e derived from technica l reasons corresponding t o c h a r a c t e r i s t ics of a p p l i c a t i o n s and lower c o s t . There are many s i z e s of LCD (Liquid Clystal Display) modules, from 0.7 inches f o r e l e c t r o n i c view f i n d e r s (EVF) t o 15 inches f o r workstat ions. Techniques of in te rconnec t ions f o r t h e s e panels have two c h a r a c t e r i s t i c s . The f i r s t i s a high dens i ty as t h e r e a r e up t o a million pixels on a panel , with each pixel needing a d r i v e r . The second i s a t h i n n e r and smaller cons t ruc t ion . So, COG technology has been developed using t h e technique of d i r e c t bonding d r i v e r ICs on panel g l a s s . The COG technology panel is not only have higher dens i ty and a t h i n n e r and smaller s i z e , but a l s o have f e w e r processes and !ower c o s t s as compared with t h e TAB (Tape Automated Bonding) technology. The former COG method of using conductive p a r t i c l e s with adhesives requi res severa l alignment processes , which made i t unsui table f o r mass prduct ion. We have inves t iga ted a new COG technology t h a t wi l l become a prospect ive winner of t h e next age. The above new COG technology must be able t o increase t h e number of I C e l e c t r o d e s , and t o decrease t h e s i z e of t h e LCD module and its c o s t . In a d d i t i o n , process of t h e above new COG technology must be simple. Some of t h e usual COG techniques needed severa l alignment processes f o r s e t t i n g of adhesives , and I C s . Also some of t h e usual COG s t r u c t u r e s were not small enough, and had some problems. We have developed t h e new COG technology cal led "MAPLE"(M1M Active Panel LSI mount Engineering) method. The MAPLE method i s a face-down bonding method t h a t bonds t h e d r i v e r I C s d i r e c t l y t o a panel g lass s u b s t r a t e using ACF (Anisotropic Conductive Film) which i s a thermoset t ing adhesive. In t h e MAPLEmethod, d r i v e r I C ch ips have s t r a i g h t Au bumps. Conductive p a r t i c l e s in t h e ACF a r e uniformly placed on t h e adhesive. "MAPLE" has only one alignment process. Using non-stationary heat t r a n s f e r ana lys i s and s t r e s s a n a l y s i s , w e ge t t h e most s u i t a b l e dynamics design and adhesive. Besides, t h e MAPLE method, rea l ized a very small f r i n g e s i z e and a t h i n , and highly r e l i a b i l e LCD module. The MAPLE method i s now being m a s s produced. 2 . A D V A N T A G E O F C O G The COG technology, which we have named t h e MAPLE method, needs t o interconnect with I C s and a panel g l a s s , which are both hard m a t e r i a l s , and need t o be highly r e l i a b i l e . The COG technology will not be used f o r var ious purposes if w e c a n ' t in terconnect both hard mater ia l s with high r e l i a b i l i t y . Developing high r e l i a b i l i t y adhesives does not always mean t h a t t h e r e l i a b i l i t y of COG technology i s high. This s tudy has been made t o increase t h e r e l i a b i l i t y of COG technology using severa l t echnica l s k i l l s . Fig.1 shows a c r o s s sec t iona l view of t h e MAPLE method model. In t h i s f i g u r e , arrows mean cons t ruc t ive forces which are drawing toge ther and des t ruc t ive forces t h a t t e a r I C s from panel g lass . Increasing construcive force and decreasing des t ruc ive force , w e have got ten high r e l i a b i l i t y . Construct ive force c o n s i s t s of t h e following: Q breaking force of adhesive. Q sur face bonding force of adhesive. @ cured construct ion force of adhesive. Destruct ive force c o n s i s t s of t h e following: Q res idua l s t r e s s ( f o r examle: res idua l s t r e s s at bonding process on acount of t h e d i f fe rence between I C s and g lass in thermal expanson) Q stress based on u s e r ' s environment. @ looseness of adhesive with humidity and heat . In t h e next place, w e explain some of above cons t ruc t ive and des t ruc t ive f o r c e s .