On Mon, 8 Jan 1996 00:46:18 -0800 Steve Allen wrote:

> From: Steve Allen <[log in to unmask]>
> Date: Mon, 8 Jan 1996 00:46:18 -0800
> Subject: plated Tin/Lead adhesion
> To: [log in to unmask]
> 
> Concerning I.R. reflowed plated Tin/Lead on single and double sided 
> PCB's.
> What can cause poor adhesion of the reflowed Tin/Lead to the plated 
> copper pad?
> Our plating process is : acid copper/h2o rinse /fluorboric 
> dip/fluorboric Tin/lead plating/ etch/ I.R. reflow.
> The "problem" is only seen on one or two panels in a particular lot, 
> and comes and goes, sometimes with months in between occurances!
> Sometimes its detected by a random tape test at pre-mask 
> inspection...sometimes, "unfortunatly" it's found after the customer 
> has assembled the PCB.  The solder joints appear to flow very well, but 
> will seperate from the copper if pressure is applied the component 
> lead.  
> No copper is attached to the solder joint that has lifted.
> The copper pad below is usually somewhat oxidized.
> We have explored many possible causes, including excessive hold time 
> between steps, etc.
> I would appreciate any thoughts on this, if anyone has some ideas...?
> 
	Steve:	There have been many good responses to your question on 
	plating adhesion however the piece of information here that I keep
	coming back to is how intermitent and selective(1-2panels)the
	problem is.I would suspect somthing more like a bad rack or anode
	more than a general chemistry problem.
	Two questions: Is the Sn/Pb thickness lower on the defective boards
	found in house?  What is the appearance of the fused Sn/Pb on these
	boards?
	
	 If you want to discuss this further please feel free to give me
	a call.We do a LOT of IR fused Sn/Pb electroplate.  
  
						Regards
						Michael Barmuta
						Staff Engineer
						Fluke Corp.
						(206)356-6076