On Fri, 18 Aug 95 17:59:03 PST [log in to unmask] wrote:

> From: [log in to unmask]> Date: Fri, 18 Aug 95 17:59:03 PST
> Subject: difficult soldering on OPC bare copper boards
> To: [log in to unmask]
> 
> 
>      We are having trouble soldering organic protective coated bare copper 
>      boards. The difficulty is occurring with manual iron soldering in the 
>      post wave/wash shop.
>      The boards soldered fine in SMT, and then they were washed. They then 
>      sat several weeks awaiting finalization of engineering changes and 
>      receipt of the EC parts. Now we are having extreme difficulty getting 
>      the solder to wet to the copper in the postmount shop.
>      Does anyone have suggestions to overcome this problem? Would it be 
>      feasible to recoat the bare copper when it's determined the boards 
>      cannot be completed immediately? Does anyone have a suggested time 
>      limit in which to complete soldering after the wash? Does anyone know 
>      of aggressive flux cored solder wire which can promote wetting and 
>      still meet Bellcore specifications?
>      Any advice would be appreciated.
>      
>      Allen Ahlert
>      [log in to unmask]
> 
	


 	 Allen: There are a couple of different approaches you can try.The   
          easiest is to try a stronger core solder.You don't specify the type 
 	  of flux activation being used.Our experience has shown most no-	
	  clean and low solids type fluxes do not do a very good job of 
	  activating copper that has seen repeated heat and chemical cycles.	
	  Try using an RMA core solder,if that doesn't work you could step up	
	  to an RA or OA type flux if they are compatible with your process-	
	  ing and end requirements.					
	  For touch-up and postsolder component attachment we have found RMA	
	  core solder does an acceptable job up to six weeks after VP reflow/	
	  clean/flowsolder/clean with our OSP coating.			
		 							
	  If the stronger flux doesn't work a different tact would be the 
	  following:			   			 	 
		           						
		1.Immerese PCA in 5% HCl 10-15 secs. 70F		
		2.Rinse 2 mins. D.I. water 80F				
		3. Repeat step 2 w/new D.I.				
		4.Rinse 30 secs. isopropyl alcohol 70F			
		5.Bake 10 mins.or till dry 220F				
	This should provide you with an active oxide free solderable surface	
	good for 24+ hrs.						
	NOTE:Caution should be taken regarding component compatibility with	
	the weak HCl and thorough cleaning to remove ionic contamination from	
	the Cl.								
									
				Regards 				
					Mike Barmuta			
						Staff Eng.		
						FLUKE Corp.		
						Everett Wa.		
						206 356 6076