Todd:I would guess your mask is too thin at the knee.When the board 
is HALed the mismatch in TCE of the copper vs soldermask is sufficeint to	
cause adhesion problems.This occurs at the weakest(i.e.thinnest)areas in this	
case the knee where the loose mask is mechanically blown off during the HAL 
operation.								
	Cross section the circuit adjacent to were the mask came off and see	
what the thickness is at the knee.I would also look at the same area prior to
HAL.You should be somewhere around 0.4-0.7 mils,the thicker the better. 
	To get a good optical measurement of the mask you need a high 
contrast between the mask and potting material of the cross section.I've had	
excellent results using white opaque highly pigmented ID ink such as 
cat-l-ink.Overcoat your cross section coupon with the ink and bake/cure prior	
to potting.This will provide you with a sharp delineation that will alllow an	
accurate measurement of mask thickness.		Good Luck!		
									
									
					Regards				
						Michael Barmuta		
						Staff Engineer		
						Fluke Corp.		
						Everett Wa.		
						(206)356-6076		
									
									
									
									
									
									
							
> Date: Thu, 2 Jan 1997 14:36:22 -0800
> Subject: Exposed circuits
> To: [log in to unmask]
> 
> Technetters,
> We have been experiencing some sporadic problems with soldermask being
> burned off the edge of the circuits at the hot air level process.  The
> soldermask on the knee of the trace seems to burn off and allows the solder
> to stick to the trace edge.  We are using a chemical clean process prior to
> soldermask, and are spraying the soldermask on with a Teledyne spray
> coater.  Has anyone else experienced these problems and what did you do to
> fix it?
> 
> Todd Rogers
> PC Boards, Inc.
> [log in to unmask]
> 
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