iLED iLED, June issue : 12

JUNE 2011 ISSUE N°1 COMP ANY INSIGHT Luminus goes large on packaging TM Paul Panaccione, Director of Packaging Technology, and Arvind Baliga, Vice-President Engineering, at Luminus Devices, talk about how their company integrates the industry's biggest LED chips into suitable formats for their customers' applications. Yo l e D e v é l o p p e m e n t : L u m i n u s D e v i c e s i s r e n own e d f o r i t s b i g, p h o t o ni c l a t t i c e , L E D c hip s . What ar e t he c halle n ge s in pac kagin g t hem? Pa u l Pa n a c c i o n e : P h o t o n ic l a t t ic e e f f ic ie n t ly e x t r ac t s light f r om t he c hip s ur f ac e, and al s o collimates the light. It direc ts the light perpendicular t o t h e c h i p' s s u r f a c e , r a t h e r t h a n i n a L a m b e r t i a n shape. We don' t want to alter the shape of that light e m i s s i o n. T h e p h o t o n i c l a t t i c e i s d e s i g n e d t o e m i t into air, it 's matc he d with the r ef r ac tive index of air c losely, and so we use an air c avit y package. We use a g l a s s w i n d o w i n t h e p a c k a g e f o r p r o t e c t i o n, s o w e n e e d t o m a ke s u r e t h a t d o e s n' t a l t e r t h e c o l l i m a t e d light using anti-r e fle c tive c oatings. T hen, our c hip a r e a i s m u c h l a r g e r t h a n a ny o t h e r L E D s o u t t h e r e . F r o m a p a c k a g i n g p e r s p e c t i ve t h e y r e s e m b l e p o w e r IC s o r p owe r t r an s i s t o r s, eve n mi c r o p r o c e s s o r s. Some of our device s ar e c lose to 100 W input power, s o we'r e di s s ip at ing 8 0 W o r s o of h e at . T he c hallenge s with big c hip ar e pr imar ily ther mal. We a d dr e s s t hat wi t h mat e r ial s an d p a c k a g e d e s i gn t hat m ay b e u n c o nve n t i o n a l i n t e r m s o f L E D p a c k a g e d e s i gn. A n o t h e r c o n c e r n wi t h b i g c hip i s C T E matching to the package, so we've done a lot of work o n ma t c h i n g ma t e r i a l s an d f i n d i n g a c o mp l i an t int e r f a c e b e t we e n t h e c hip a n d t h e p a c k a g e. In addition, our devic e s emit a lot of light, 15 W or s o, a n d w e h a v e t o m a ke s u r e t h e p a c k a g e c a n h a n d l e t hat . YD: To what de gr e e ar e you able to me et t he se c h al l e n g e s wi t h c o mm e r c i al l y -a va i l ab l e pac kaging materials? P P: We ' v e h a d t o w o r k v e r y c l o s e l y w i t h o u r s u p p l i e r s o n d ev e l o p i n g n e w m a t e r i a l s . We ' v e f o r m e d p a r t n e r s h i p s w i t h o u r ke y s u p p l i e r s w h e r e we s har e r o a dmap s an d c hall e n g e s. A s a r e s ul t we' ve a c t uall y d eve l o p e d a f ew n ew o r imp r ove d m a t e r i a l s . I t h a s t a ke n a w h i l e – a l o t o f w o r k a n d a l o t o f c o -o p e r a t i o n – b u t i t 's r e s u l t e d i n s o m e p r e t t y innovative and suc c e s s f ul mater ial development. Y D : A r e t h e r e a ny e x a m p l e s t h a t y o u c a n t a l k ab ou t ? PP: We've wor ke d ver y c los ely with our die-at t ac h supplier in developing a higher thermal conduc tivit y, l o w e r m o d u l u s m a t e r i a l t h a t w i l l b o t h g i ve u s b e t t e r thermal conduc tivit y and accommodate the thermal mismatc h bet we en c hip and pac kage muc h bet ter. We've be en r unning that mater ial in our pr oduc t for a c ouple of year s now with ver y high r eliabilit y. On our pac kage d subs tr ate it s elf, we ne e d a diele c tr ic mat e r ial in o ur p a c k a g e t o s e p ar at e e l e c t r i c al t r a c e s b u t t hat al s o hap p e n s t o f all wi t hin t h e t h e r mal p at h in s ome c as e s. We've wor ke d on developing high-t h e r mal c o n du c t i v i t y di e l e c t r i c mat e r ial t hat ha s enable d higher br ightne s s. YD: What are the key packaging material areas t hat you're foc using on wher e mor e impr ovement is s t ill ne e de d? P P: T h e r m a l a l way s c o m e s t o m i n d fi r s t f o r m e, be c aus e the s e ar e suc h high power devic e s. R ight now we are working with one of our thermal inter face m a t e r i a l s u p p l i e r s a n d a c t u a l l y d ev e l o p i n g a mate r ial that has an or de r of magnit ude highe r t h e r m a l c o n d u c t i v i t y t h a n w h a t we'r e c ur r e n t l y u s i n g. T h a t ' s g o i n g t o a l l o w u s t o d r i v e t h e c h i p s a t eve n highe r br ight ne s s, r e duc e t he r mal r oll-ove r a n d a l l o w h i g h e r d r i ve c u r r e n t s . A s a r e s u l t w e'r e g o i n g t o b e l o o k i n g a t a 20 p e r c e n t o r s o b o o s t i n br ightne s s. We'r e going to be c oming out with that in t h e n e x t s i x t o nin e m o nt h s. Y D: How do e s applic at ion in flue nc e pac kage de sign? A r v i n d B a l i g a : O n e w ay t o l o o k a t t h e p a c k a g e i s t h a t i t 's t h e i n t e r f a c e t o t h e a p p l i c a t i o n. It 's t h e ther mal, optic al and ele c tr ic al inter fac e. We wor k Arvind Baliga, Vice-President of Engineering, Luminus Devices Paul Panaccione, Director of Packaging Technology, Luminus Devices One size fits all: For projection applications like those its Luminus Devices can tailor LED chip sizes of products like its SBT-16 LEDs to the shape of customers’ microdisplays without needing to change the package. (Courtesy of Luminus Devices) 12 i LED

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