"Davis, Phil" <[log in to unmask]> Wrote:
| Phil Davis
| Manager Mechanical Engineering & Packaging
| Wilcox Electric, Inc
| 
| We are looking at eliminatingng the gold plating on 
| some large (18" x 24") 
| microstrip boards by having the supplier coat the 
| boards with ENTEK. These 
| microstrips are on Teflon (GXN) substrate.
| 
| 1) Does anyone have experience using ENTEK on Teflon 
| sunstrate?

Generally GXN Teflon is used where electrical signals are of 
primary concern.  In most cases (95% +) the traces on Teflon 
boards are not covered by soldermask because of the electrical 
performance desired.  There are however some Teflon boards that 
cover the traces with soldermask (embedded microstrip).

If your Teflon board has soldermask over the traces, you should 
have no problem using ENTEK in IR reflow.  Assuming that the 
assembly process has been set up for ENTEK coated boards.

If your board doesn't have the traces covered with soldermask, 
then it depends on if you want exposed copper traces.  ENTEK is a 
temporary coating that has a 12 month shelf life in preserving the 
copper for solderability.  The traces of the board will be 
protected from the environment by the ENTEK.  It would depend on 
the environment where the board will be used and whether or not 
you sit in the camp that believes exposed copper on finished 
boards is OK.  I think the jury is still out on exposed copper.  
I have limited data supporting either side (exposed copper is OK 
vs exposed copper is detrimental).  I am sure that there are 
applications where each is justified.  I welcome others to comment 
on this issue.  

| 
| 2) Can we IR reflow the components to the board while 
| using ENTEK? Do we 
| need to remove the ENTEK before assembly?

ENTEK is a thin organic coating that is intended to protect the 
surface of the copper until the assembly, generally it is called 
OSP (organic solderability preservative) ENTEK being a trade name. 
 The flux used in assembly attacks the surface of OSP allowing the 
solder to bond directly to the copper surface.  

As a board manufacturer, we are only aware of 1 customer out of 
many using ENTEK that had problems with IR reflow on an OSP 
surface.  The solder paste used had an antislump agent in it that 
inhibited the flux from attacking the OSP.  After changing the 
paste, there were no problems.

Using OSP in wave solder assembly may need process adjustments to 
allow the board sufficient time to remain in contact with the flux 
to remove the OSP.  ENTEK has been used successfully in many 
assembly houses using wave solder as an assembly method.

I can give you a couple of contacts if you need more information 
as well as a couple of reports regarding ENTEK.

Darren Hitchcock
Merix Corporation
Forest Grove, Oregon

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(503)359-2658