RE>REQ: Info on Entek Plus/NC Flux           2/2/96

Jon,
Excellent note regarding Entek Plus on flex.  

We've used both Entek Plus and MacDermid M-Coat Plus for a couple of years now with no-clean chemistries with generally no problems.  (We tried a couple of other formulations, as well.)  A couple of initial problems, though:

1) Defects (opens) at CBGA sites because of "locally thick" OSP coating.  The supplier claimed that the coating cannot exceed a certain thickness, but I believe that this is on well-controlled flat coupons.  On our boards you could see how some of the pads developed a "shellac-like" finish because of the excess thickness - lab measurements indicated that it was ~3x the max thickness.  We attributed this to both the OSP application process and the via geometry, which allowed residual coating to seep onto the BGA pads toward the end of the process.  Changing the application process worked.

2) We found that the OSP-coated boards had to be *absolutely dry* prior to bagging and shipping.  Any moisture left in the vias would seep out and destroy the OSP coating (it turns black).

The only real concerns to date are the lack of a good topside PTH fillet and lack of good solder spread on pads.   

Also:  we have had customers question the reliability of exposed copper, but there is a large volume of data within the industry which helped us to successfully address these concerns.  
 
Regards,
Greg Bartlett
Mercury Computer Systems
Chelmsford, MA  
----------------
Text of previous message:

Being an Application Engineer supporting Flex and
Rigid-flex product for Merix Corporation, I always
get nervous when comments are made regarding things
that "cannot be done" on flex circuitry. 

At Merix, one of our largest flex circuit programs
uses the Entek 106A process. This flex application,
as well as others that have used the Entek OSP surface 
finish, have proven to be very compatible with our customers
assembly processes and flex assembly processes at Merix. 

Furthermore, the process for applying the Entek
OSP surface finish is extremely compatible with 
flex circuit processing. Especially if you are comparing
it to the mechanical and thermal stresses inherent to other 
surface finish application processes (ie: HASL).


I do not want to suggest that the Entek system will work in 
every application. If I knew of such a system, Merix wouldn't
need Applications Engineers like me.

If you have specific questions about using Entek
surface finishes on flex circuits, feel free
to contact me at Merix Corp:

      <a href="/scripts/wa.exe?LOGON=A3%3Dind96%26L%3DTECHNET%26E%3Dquoted-printable%26P%3D667606%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DISO-8859-1%3B%2520name%3D%2522Message%2520Body%2522%26N%3DMessage%2520Body" target="_parent" >[log in to unmask]</a>

I would be happy to discuss the compatibility of our 
Entek 106A with your assembly processes.

If you have generic questions around Entek, 
N/C process compatibility, etc. I would suggest 
that you contact Enthone directly. A name you can 
start with is:

      Bret Taucher
      Enthone
      206/222-6629


Thank for you time,
  Jon Woodyard,  Applications Engineer
  Merix Corporation
  503/359-2623
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---------Original Message---------------------------------------
| _________________________________
| Subject: Re: REQ: Info on Entek Plus/NC Flux
| Author:  <a href="/scripts/wa.exe?LOGON=A3%3Dind96%26L%3DTECHNET%26E%3Dquoted-printable%26P%3D667606%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DISO-8859-1%3B%2520name%3D%2522Message%2520Body%2522%26N%3DMessage%2520Body" target="_parent" >[log in to unmask]</a> at corp
| Date:    1/31/96 7:58 PM
| 
| 
| I worked for a flex manufacture that was trying to get Entek 
| approved.  It's 
| almost imposible with flex.  I don't recommend it.  Be sure 
| your spec. is 
| clear about ridgid only.
|  
|