There are a number of published papers on the subject -- suggest you do a 
literature search.  No-clean assembly may require tighter process controls 
and possibly changing to an OSP compatible no-clean flux.  I would also 
recommend working with your PCB shop/OSP supplier to address specific 
issues.  I found our OSP supplier very helpful for providing support 
on assembly-related technical "roadblocks".


Dave Boggs
Merix Corporation
phone:  (503) 359-9300
fax:  (503) 359-1181





[log in to unmask] Wrote:
| 
| 
| I would greatly appreciate any input regarding changing from 
| HASL to OSP.  We assemble heavy copper boards and are 
| experiencing difficulties as we move to 0805 chip packages.  
| We 
| are comtemplating changing to OSP to alleviate some of the 
| pain.  I would appreciate any info regarding process changes 
| we 
| may have to make (pad design, pre-heat, flux application 
| method, etc).  A typical application is 4 layer board with 2 
| oz. internals and 2 oz. externals plated to 3 oz.  Three 
| thermal cycles (top side reflow, bottom side epoxy cure, and 
| wave solder).  SOIC and SOT-23 on top, 0805 on bottom, plus 
| through hole components.  No-clean paste and wave solder 
| flux, 
| wave flux applied by foaming on most machines but spray 
| fluxer 
| also available.  Assemblies have high thermal mass (large 
| magnetics and heatsinks).  Thanks for your help.
| 
| Pat Bailey
| Zytec Corporation
| phone 507 637-2966 x355
| fax 507 644-3720
| e-mail [log in to unmask]
|