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1 I n t r o d u c t i o n      

Lead frame (Copper Alloy)

IC (Silicon)Die Attach (Epoxy)

Lead frameDie Pad (or thermal pad)− Exposed At Base of the Package

Mold Compound (Epoxy)

A p p l i c a t i o n R e p o r t    S L O A 1 2 0 – M a y 2 0 0 6        

P o w e r P A D ™ L a y o u t G u i d e l i n e s      Y a n g B o o n Q u e k        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    H P L A u d i o P o w e r A m p l i f i e r s      

A B S T R A C T        

T h i s a p p l i c a t i o n r e p o r t f o c u s e s o n h e l p i n g p r i n t e d - c i r c u i t b o a r d d e s i g n e r s t o u n d e r s t a n d      a n d b e t t e r u s e b o a r d l a y o u t a n d s t e n c i l i n f o r m a t i o n f o r T e x a s I n s t r u m e n t s P o w e r P A D ™          d e v i c e s .  

B o a r d l a y o u t a n d s t e n c i l i n f o r m a t i o n f o r m o s t T e x a s I n s t r u m e n t s ( T I ) P o w e r P A D ™ d e v i c e s i s p r o v i d e d i n      t h e i r d a t a s h e e t s . T h i s d o c u m e n t f o c u s e s o n h e l p i n g p r i n t e d - c i r c u i t b o a r d ( P C B ) d e s i g n e r s u n d e r s t a n d a n d      b e t t e r u s e t h i s i n f o r m a t i o n f o r o p t i m a l d e s i g n s .  

T h e P o w e r P A D p a c k a g e i s a t h e r m a l l y e n h a n c e d , s t a n d a r d - s i z e I C p a c k a g e d e s i g n e d t o e l i m i n a t e t h e u s e      o f b u l k y h e a t s i n k s a n d s l u g s . T h i s p a c k a g e c a n b e e a s i l y m o u n t e d u s i n g s t a n d a r d P C B a s s e m b l y      t e c h n i q u e s a n d c a n b e r e m o v e d a n d r e p l a c e d u s i n g s t a n d a r d r e p a i r p r o c e d u r e s .  

T h e P o w e r P A D p a c k a g e i s d e s i g n e d s o t h a t t h e l e a d f r a m e d i e p a d ( o r t h e r m a l p a d ) i s e x p o s e d o n t h e      b o t t o m o f t h e I C ( s e e        F i g u r e 1      ) . T h i s p r o v i d e s a n e x t r e m e l y l o w t h e r m a l r e s i s t a n c e (      θ      J C      ) p a t h b e t w e e n t h e      d i e a n d t h e e x t e r i o r o f t h e p a c k a g e .  

F i g u r e 1 . S e c t i o n V i e w o f a P o w e r P A D P a c k a g e      

P o w e r P A D i s a t r a d e m a r k o f T e x a s I n s t r u m e n t s .  

S L O A 1 2 0 – M a y 2 0 0 6         P o w e r P A D ™ L a y o u t G u i d e l i n e s        1  

S u b m i t D o c u m e n t a t i o n F e e d b a c k      

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2 B o a r d L a y o u t    

Thermal Via

Copper area

2 . 1 S o l d e r M a s k D e f i n e d T h e r m a l P a d        

2 . 2 C o p p e r A r e a s        

2 . 3 T h e r m a l V i a s        

B o a r d L a y o u t    

F i g u r e 2        s h o w s a n e x a m p l e o f t h e r e c o m m e n d e d b o a r d l a y o u t f o r a P C B p a c k a g e .  

F i g u r e 2 . B o a r d L a y o u t f o r a P C B P a c k a g e      

T h e s o l d e r m a s k d e f i n e d t h e r m a l p a d i s t h e e x p o s e d c o p p e r a r e a n o t c o v e r e d b y s o l d e r m a s k . I t m u s t b e      s o l d e r e d d i r e c t l y t o t h e t h e r m a l p a d o n t h e b o t t o m o f t h e I C . A n e x a m p l e o f t h e r e c o m m e n d e d d i m e n s i o n s      i s s h o w n i n        F i g u r e 2        . 

C o p p e r a r e a s o n a n d i n t h e P C B a c t a s h e a t s i n k s f o r t h e P o w e r P A D d e v i c e . T o p c o p p e r a r e a s s h o u l d b e      c o v e r e d w i t h s o l d e r m a s k l e a v i n g o n l y t h e s o l d e r m a s k d e f i n e d t h e r m a l p a d e x p o s e d . T h e t o p c o p p e r    a r e a s s h o u l d b e m a d e a s l a r g e a s p o s s i b l e .  

I n n e r o r b o t t o m - l a y e r c o p p e r p l a n e s c a n a l s o b e c o n n e c t e d t o t h e t h e r m a l p a d b y u s i n g v i a s a n d s h o u l d      b e m a d e a s l a r g e a s p o s s i b l e . T h e t h e r m a l p a d i s u s u a l l y t i e d t o g r o u n d , a n d d e s i g n e r s s h o u l d e n s u r e      e l e c t r i c a l c o r r e c t n e s s w h e n c o n n e c t i n g t h e c o p p e r p l a n e s t o t h e t h e r m a l p a d .  

D e s i g n e r s m a y l e a v e t h e b o t t o m c o p p e r p l a n e e x p o s e d . H o w e v e r , s t u d i e s h a v e s h o w n t h a t t h i s h a s      m i n i m a l i m p a c t o n t h e r m a l p e r f o r m a n c e .  

T I r e c o m m e n d s p l a c i n g t h e r m a l v i a s i n t h e s o l d e r m a s k d e f i n e d t h e r m a l p a d t o e f f e c t i v e l y t r a n s f e r h e a t    f r o m t h e t o p c o p p e r l a y e r o f t h e P C B t o t h e i n n e r o r b o t t o m c o p p e r l a y e r s .  

T h e t h e r m a l v i a s s h o u l d m a k e t h e i r c o n n e c t i o n t o t h e i n t e r n a l g r o u n d p l a n e w i t h a c o m p l e t e c o n n e c t i o n      a r o u n d t h e e n t i r e c i r c u m f e r e n c e o f t h e p l a t e d t h r o u g h h o l e . P l a c e a r i n g o f e x p o s e d c o p p e r ( 0 , 0 5 m m        w i d e ) a r o u n d t h e v i a s a t t h e b o t t o m c o p p e r p l a n e .  

D o n o t c o v e r t h e v i a s w i t h s o l d e r m a s k w h i c h c a u s e s e x c e s s i v e v o i d i n g .  

D o n o t u s e a t h e r m a l r e l i e f w e b o r s p o k e c o n n e c t i o n w h i c h i m p e d e s t h e c o n d u c t i o n p a t h i n t o t h e i n n e r    

c o p p e r l a y e r ( s ) .  

2      P o w e r P A D ™ L a y o u t G u i d e l i n e s         S L O A 1 2 0 – M a y 2 0 0 6    

S u b m i t D o c u m e n t a t i o n F e e d b a c k      

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Web or Spoke ViaNOT Recommended

Solid   Via

Recommended

Exposed copper  –

0.05mm around via

TopCopper Area –makeas large as possible

Solder Mask Defined Thermal Pad –   follow

dimensions given

Bottom   metal

Plane – make as

large as possible

Thermal Vias -follow spacinggiven and keepdiameters less thanor equal to 0,3 mm

B o a r d L a y o u t    

F i g u r e 3 . V i a C o n n e c t i o n a t t h e b o t t o m c o p p e r p l a n e      

T I p r o v i d e s t h e r e c o m m e n d e d l a y o u t o f t h e t h e r m a l v i a s i n m o s t d a t a s h e e t s . T h e r e c o m m e n d e d v i a      d i a m e t e r i s 0 , 3 m m o r l e s s , a n d t h e r e c o m m e n d e d v i a s p a c i n g i s 1 m m ( s e e        F i g u r e 2        a n d     F i g u r e 4        ) . 

F i g u r e 4 . X - R a y – D G N D e v i c e      

V i a s m a y b e p l u g g e d t o p r e v e n t s o l d e r l o s s a n d p r o t r u s i o n s . T h i s o f t e n p r o d u c e s t h e b e s t t h e r m a l  p e r f o r m a n c e s b u t i s n o t n e c e s s a r y o r r e c o m m e n d e d b e c a u s e o f t h e i n c r e a s e d c o s t o f P C B b o a r d s a n d      b e c a u s e s o l d e r t e n d s t o w e t t h e u p p e r s u r f a c e f i r s t b e f o r e f i l l i n g t h e v i a s .  

V i a s c a n a l s o b e u s e d i n t h e c o p p e r a r e a o u t s i d e t h e s o l d e r m a s k d e f i n e d t h e r m a l p a d t o h e l p t r a n s f e r    h e a t t o t h e b o t t o m o r i n n e r p l a n e s ( s e e        F i g u r e 5        ) . 

S L O A 1 2 0 – M a y 2 0 0 6         P o w e r P A D ™ L a y o u t G u i d e l i n e s        3   

S u b m i t D o c u m e n t a t i o n F e e d b a c k      

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Thermal Via -keep diametersless than or equal to 0,3 mm

External

 Via

 Via

filled

with

solder 

Unfilled Via

Solder Mask

Defined Thermal

Pad

TopCopper Area

Only externalvias are used

2 . 4 S o l d e r L o s s a n d P r o t r u s i o n s        

B o a r d L a y o u t    

F i g u r e 5 . X - R a y – P C B D e v i c e W i t h I n t e r n a l a n d E x t e r n a l V i a s      

I f t h i n P C B b o a r d s o r v i a s l a r g e r t h a n 0 , 3 m m a r e u s e d , d e s i g n e r s m a y u s e o n l y e x t e r n a l v i a s t o p r e v e n t    

s o l d e r l o s s a n d p r o t r u s i o n s ( s e e        F i g u r e 6        ) . D e s i g n e r s s h o u l d n o t e t h a t t h i s m i g h t r e d u c e t h e r m a l  p e r f o r m a n c e s i g n i f i c a n t l y a n d s h o u l d b e e v a l u a t e d o n t h e i r P C B s .  

F i g u r e 6 . E x a m p l e o f U s i n g O n l y E x t e r n a l V i a s      

S o l d e r l o s s a n d p r o t r u s i o n s r e s u l t w h e n e x c e s s i v e s o l d e r f l o w e d t h r o u g h i n t e r n a l v i a s d u r i n g r e f l o w . T h e s e      u s u a l l y h a p p e n w h e n i n c o r r e c t i n t e r n a l v i a s s i z e s a n d s t e n c i l o p e n i n g s a r e u s e d .  

S o l d e r l o s s r e s u l t s i n v o i d i n g a n d s e v e r e l y a f f e c t s t h e r m a l c o n d u c t i v i t y . D e s i g n e r s a r e e n c o u r a g e d t o x - r a y      t h e i r r e f l o w e d b o a r d s t o v e r i f y t h a t a t l e a s t 5 0 % o f t h e r m a l p a d a r e a i s s o l d e r e d ( l e s s t h a n 5 0 % v o i d i n g )    w h e n u s i n g 0 , 1 2 7 - m m - t h i c k s t e n c i l s .  

P r o t r u s i o n s m i g h t c a u s e m i s a l i g n m e n t i n s t e n c i l o n t h e r e v e r s e s i d e o f P C B ( s e e        F i g u r e 7        ) . 

4      P o w e r P A D ™ L a y o u t G u i d e l i n e s         S L O A 1 2 0 – M a y 2 0 0 6    

S u b m i t D o c u m e n t a t i o n F e e d b a c k      

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Protrusion

2 . 5 S t e n c i l    

B o a r d L a y o u t    

F i g u r e 7 . P r o t r u s i o n a t t h e O t h e r S i d e o f B o a r d      

F i g u r e 8        s h o w s a n e x a m p l e o f t h e r e c o m m e n d e d s t e n c i l o p e n i n g s a n d t h i c k n e s s . F o l l o w t h e s t e n c i l  o p e n i n g s a n d t h i c k n e s s r e c o m m e n d a t i o n s t o e n s u r e t h a t t h e r i g h t a m o u n t o f s o l d e r p a s t e i s u s e d .  

F i g u r e 8 . R e c o m m e n d e d S t e n c i l O p e n i n g s f o r P C B P a c k a g e      

F o r P o w e r P A D d e v i c e s , d o n o t u s e c r o s s h a t c h i n g i n t h e s t e n c i l t h e r m a l p a d o p e n i n g . T h i s s i g n i f i c a n t l y      r e d u c e s t h e a m o u n t o f s o l d e r p a s t e a p p l i e d a n d i n c r e a s e s v o i d i n g ( s e e        F i g u r e 9        ) . 

S L O A 1 2 0 – M a y 2 0 0 6         P o w e r P A D ™ L a y o u t G u i d e l i n e s        5   

S u b m i t D o c u m e n t a t i o n F e e d b a c k      

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Solder  paste  appliedNo  solder  paste  applied

Cr oss Hatching – Not   r ecommended

No Cr oss Hatching – Recommended

2 . 6 R e c o m m e n d e d S o l d e r P a s t e        

2 . 7 A d d i t i o n a l I n f o r m a t i o n        

B o a r d L a y o u t    

F i g u r e 9 . S t e n c i l T h e r m a l P a d O p e n i n g      

T I r e c o m m e n d s u s i n g t y p e 3 o r f i n e r s o l d e r p a s t e w h e n m o u n t i n g a P o w e r P A D .  

F o r d e t a i l e d i n f o r m a t i o n o n t h e P o w e r P A D p a c k a g e i n c l u d i n g t h e r m a l m o d e l i n g c o n s i d e r a t i o n s a n d r e p a i r    p r o c e d u r e s , s e e t h e        P o w e r P A D T h e r m a l l y E n h a n c e d P a c k a g e        a p p l i c a t i o n r e p o r t (      S L M A 0 0 2        )  

6      P o w e r P A D ™ L a y o u t G u i d e l i n e s         S L O A 1 2 0 – M a y 2 0 0 6    

S u b m i t D o c u m e n t a t i o n F e e d b a c k      

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