Heatsink Design Flow
f or E M C
Jinghan Y u , C is c o S y s t e m s
P hil ip p e S o c ho u x , C is c o S y s t e m s
A l p e s h B ho b e , C is c o S y s t e m s
F e d e r ic o C e nt o l a, F l o m e r ic s
F e b r u ar y 6 , 2 0 0 8
P r e s e n ta tio n _ ID
©2 0 0 6 C is c o S y s te m s , In c . A ll r ig h ts r e s e r v e d .
C is c o C o n fid e n tia l
1
Motivation
•H e a ts in k s a r e la r g e c o n d u c tiv e o b je c ts , t y p ic a lly u n g r o u n d e d , a n d p la c e d
a b o v e A S IC s o r o th e r IC s
•T h e y m a y p ic k u p a n d e n h a n c e r a d ia tio n
• W i t h t o d a y ’s S e r D e s l i n e r a t e s , w a v e l e n g t h s i z e s i n t h e s y s t e m
c o m p a r a b le to h e a ts in k s iz e s
a re n o w
2
E MI and H e ats ink s
Heatsink
D ie
N o n -c o n d u c t i v e e p o x y
T IM
P C B
H i g h -s p e e d s u r f a c e r o u t i n g
A S I C P a c k a g e ( v ia s , t r a n s m is s io n lin e s , p la n e s )
E le c t r ic a lly c o n d u c t iv e t h e r m a l lid
3
H e ats ink D e s ig n F l ow
•T h e h e a ts in k d e s ig n fo r E M I is o fte n le ft to lu c k
•E M C e n g in e e r s b e c o m e in v o lv e d a t th e e n d o f th e d e s ig n w h e n a p r o b le m
is d is c o v e r e d
•M a n y s tu d ie s h a v e b e e n d o n e o n h e a ts in k r a d ia tio n
•N o d e s ig n m e th o d o lo g y o f h e a ts in k d e s ig n
•H o w to a p p ly t h is r e s e a r c h to r e d u c e E M I fr o m
s y s te m a tic fa s h io n ?
h e a ts in k s o n p r o d u c ts in a
4
H e ats ink D e s ig n F l ow
P r e -L a y o u t
E M I lo o k u p ta b le s
A v o id m a jo r
re s o n a n c e p e a k s ?
No
Y e s
P o s t L a
v e r ific a tio
a d ju s t
n e c e s s
F e e d b a c k
L a b -s i m u l a t i o n
c o r r e la t io n s tu d ie s
y o u t
n a n d
a s
a ry
F a b o u t
5
A s s u m p tions
T h e h e a ts in k d e s ig n flo w is b u ilt o n th e fo llo w in g a s s u m p tio n s :
•A S IC
I/O
d a ta r a te s a r e k n o w n b e fo r e th e P C B la y o u t b e g in s
•H e a ts in k s iz e a d ju s tm e n ts c a n b e m a d e p r io r to P C B p la c e m e n t fr e e z e
•C o o lin g e ffe c tiv e n e s s c a n b e a c h ie v e d w ith d iffe r e n t E M I p e r fo r m a n c e s
6
H e ats ink
•S o m e h e a ts in k d im e n s io n s r e m a in c o n s ta n t
• 3 o t h e r d i m e n s i o n s m a y v a r y : H e i g h t , D e p t h , a n d W i d t h (n u m b e r o f f i n s )
7
U nl oad e d C as e
• T h e f i n h e i g h t (H ) v a r i e d f r o m
0 .12 t o 0 .9 2 i n c h e s
• T h e d e p t h (D ) o f t h e h e a t s i n k c a n v a r y f r o m
0 .6 1 t o 1.9 6 i n c h e s
• T h e w i d t h (W ) , w h i c h i s d r i v e n b y t h e n u m b e r o f f i n s o n t h e h e a t s i n k , c a n
v a r y f r o m 0 .6 1 t o 7 i n c h e s .
8
S im u l ation D atab as e
S e le c te d h e a ts in k s iz e s :
• D e p t h : 0 .6 1, 0 .7 6 , 0 .9 1, 1.0 6 , 1.2 1, 1.3 6 , 1.5 1, 1.6 6 , 1.8 1, 1.9 6 i n c h e s
• H e i g h t : 0 .12 , 0 .5 2 , 0 .9 2 i n c h e s
• W i d t h (n u m b e r o f f i n s ) : t h e r a n g e v a r i e d a c c o r d i n g t o t h e D e p t h
•P o p u la tio n m a tr ix o f 4 6 5 c a s e s
•S im u la te e a c h c a s e in d e p e n d e n tly
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S im u l ation E nvir onm e nt
•S o u r c e is lo c a te d in th e c e n t e r o f th e h e a ts in k
• 1-V d i p o l e s o u r c e b e t w e e n t h e h e a t s i n k a n d t h e P C B g r o u n d p l a n e
•F la t s o u r c e s p e c tr u m
b e t w e e n 1 – 15 G H z
• D i s t a n c e b e t w e e n t h e P C B g r o u n d p l a n e a n d t h e h e a t s i n k = 0 .1”
•In fin ite ly la r g e g r o u n d p la n e a n d p e r fe c tly c o n d u c tiv e
•V a r ie d c a p a c it a n c e b e t w e e n h e a ts in k a n d P C B g r o u n d p la n e w ith o u t a n y
s ig n ific a n t c h a n g e to th e r e s u lts .
1 0
H e ats ink D e s ig n E x am p l e
•
H e a ts in k fo r A S IC
w i t h S e r D e s s p e e d 6 .2 5 G b / s (frequencies under
co nsidera t io n a re 6 . 2 5 , 9 . 3 7 5 , 1 2 . 5 G H z )
•
H e a t s i n k D e p t h (D ) i s 1.0 6 ”
•
H e i g h t : 0 .12 , 0 .5 2 , 0 .9 2 ”
•
W i d t h (n u m b e r o f f i n s ) : 10 – 3 4 (f i n s a r e a d d e d i n p a i r s )
1 1
E MI P l ots
F ix e d D e p th
3 H e ig h ts ( 0
V a r ia b le n u m
F re q u e n c y =
( 1 . 0 6 ”)
.1 2 , 0 .5 2 , 0 .9 2 )
b e r of f i n s
6 .2 5 G H z
1 2
E MI P l ots
F ix e d D e p th
3 H e ig h ts ( 0
V a r ia b le n u m
F re q u e n c y =
( 1 . 0 6 ”)
.1 2 , 0 .5 2 , 0 .9 2 )
b e r of f i n s
9 .3 7 5 G H z
1 3
E MI P l ots
F ix e d D e p th
3 H e ig h ts ( 0
V a r ia b le n u m
F re q u e n c y =
( 1 . 0 6 ”)
. 1 2 , 0 . 5 2 , 0 . 9 2 ”)
b e r of f i n s
1 2 .5 G H z
1 4
C or r e l ation w ith L ab
•V a lid a te th e a c c u r a c y o f th e M ic r o s tr ip e s
TM
s o ftw a re
•T h e h e a t s in k w a s e x c ite d a t d is c r e te fr e q u e n c ie s r a n g in g fr o m
15 G H z i n s t e p s o f 5 0 0 M H z
•T h e r e s u ltin g f ie ld s tr e n g th w a s m e a s u r e d u s in g a S p e c tr u m
1G H z to
A n a ly z e r
1 5
C or r e l ation w ith L ab
0 d e g r e e a n g le
4 5 d e g r e e a n g le
4 5 d e g r e e a n g le
9 0 d e g r e e a n g le
1 6
E f f e c ts of L oad ing
•In a n a c tu a l a p p lic a tio n , a d d itio n a l h e a ts in k s a r e p la c e d n e a r th e h e a ts in k
u n d e r c o n s id e r a tio n
•T h e a d d itio n a l m e ta llic s tr u c tu r e s w ill in flu e n c e th e c u r r e n t d is tr ib u tio n o n
th e h e a ts in k a n d th e r e fo r e its to ta l r a d ia te d p o w e r
•T h e fo llo w in g s tu d y a p p r o x im a te s th e e ffe c ts o f h a v in g a d d it io n a l h e a ts in k s
n e a r b y in s id e a c h a s s is
1 7
E f f e c ts of L oad ing
H e a ts in k
G r o u n d p la n e
W a ll o f c o n d u c t iv e m a te r ia l
• S u r r o u n d t h e h e a t s i n k w i t h a “p i c t u r e f r a m e ” o f p e r f e c t l y c o n d u c t i v e
m a te r ia l to a p p r o x im a te a w o r s t c a s e s c e n a r io
• D i s t a n c e s o f 1, 3 a n d 5 i n c h e s f r o m
1.2 6 i n c h e s
t h e h e a t s i n k o f b a s e w i d t h s o f 0 .9 1 a n d
• T h i s p r o v i d e s insight i n t o h o w m u c h t h e t o t a l r a d i a t e d p o w e r w i l l v a r y w h e n
th e h e a t s in k is p la c e d w it h in a c h a s s is w ith o th e r h e a ts in k s n e a r b y
1 8
E f f e c ts of L oad ing
1 9
E f f e c ts of L oad ing
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E f f e c ts of L oad ing
•T h e r e is little v a r ia tio n in to ta l r a d ia te d p o w e r fr o m th e h e a ts in k w h e n th e
p ic tu r e fr a m e is fu r th e r th a n 3 in c h e s a w a y fr o m th e h e a ts in k
•T h e r e is little v a r ia tio n in to ta l r a d ia te d p o w e r fr o m
h e ig h t o f th e p ic tu r e fr a m e is s m a ll
th e h e a ts in k w h e n th e
•T h e r e a r e a v e r y la r g e n u m b e r o f p o s s ib le c o m b in a tio n s o f h e a ts in k s a n d it
is n o t fe a s ib le to s im u la te e a c h p o s s ib ilit y
•T h e r e fo r e it is a lw a y s r e c o m m e n d e d to p e r fo r m
th e h e a t s in k in s id e th e c h a s s is
a p o s t la y o u t s im u la tio n o f
21
D e s ig n F l ow
E x am p l e
A h e a t s i n k w i t h 14 f i n s s u r r o u n d e d b y o t h e r h e a t s i n k s
22
D e s ig n F l ow
F ix e d D e p th
3 H e ig h ts ( 0
V a r ia b le n u m
F re q u e n c y =
E x am p l e
( 1 . 0 6 ”)
.1 2 , 0 .5 2 , 0 .9 2 )
b e r of f i n s
6 .2 5 G H z
23
D e s ig n F l ow
A d d 8 f i n s t o r e d u c e E M I a t 6 .2 5 0 G H z
E x am p l e
24
P os t L ay ou t V e r if ic ation
25
C onc l u s ion
•A d e s ig n flo w is p r o p o s e d th a t w ill a llo w q u ic k a n d s y s te m a tic s im u la tio n s o f
h e a ts in k fo r E M I
•A la r g e n u m b e r o f h e a t s in k s iz e s h a v e b e e n s im u la te d a n d t h e r e s u lts a r e
o r g a n iz e d in lo o k u p ta b le o r p lo ts
•G o o d c o r r e la tio n s to la b m e a s u r e m e n ts a r e o b ta in e d
•T h e e ffe c ts o f e le c tr o m a g n e tic a lly lo a d in g th e h e a ts in k a r e s tu d ie d
•A d d itio n a l r e s e a r c h is n e e d e d
•T h e a u th o r s b e lie v e th a t th is m e th o d o lo g y w ill b e a b le to p r o v id e s ig n ific a n t
g u id a n c e fo r h e a ts in k d e s ig n fo r E M C
26
A c k now l e d g e m e nts
•W e w o u ld lik e to th a n k F u ji F u jiy a m a fr o m
s u p p o r t a n d h e lp w ith la b m e a s u r e m e n ts .
C is c o S y s te m s f o r h is te c h n ic a l
•W e w o u ld a ls o lik e to th a n k th e fo llo w in g C is c o M e c h a n ic a l E n g in e e r s fo r
p r o v i d i n g u s w i t h t h e i n i t i a l d i m e n s i o n s o f h e a t s i n k s : H -S L i a n g , F r a n s
K u s n a d i, a n d S u s h e e la N a r a s im h a n .
27