I did a design of experiment on Entek Plus Cu-106A. we used WS paste and 
  the board was a 2 side, 8-layer rigid-flex board w/ only 1 
  fountain-soldered TH component. Since we did not use no-clean process, I 
  could not offer help on some of your Qs.
  
  2. Marginal effect of storgae time. We found little difference btwn days 
  and 1 year storage time on solderability. I think factory environment(~30C 
  and 50%) is OK. Our guideline is storage < 1 month.
  
  3. Highly recommend N2 use, especially if you use no-clean.
  
  4. Hold time btwn reflows is the most significant factor on solderability. 
  Try to minimize it. We recommended < 12 hrs for our supplier.
  
  5. We use in-line aqueous cleaner to clean misprint.
  
  6  Other considerations: 
     Prebake in N2.
     Be careful about misprint clean. Read the Spec. for Entek Plus, most 
     solvents remove some of OSP. Even water clean (140F) can move ~15% of 
     OSP. We used water clean and found that it did remove some of the OSP. 
     However, the remaining OSP is thick enough to preserve solderability.
     To eliminate test and other concerns, we covered all test points and 
     ground rings with solder.
  
  Yuan Li
  Exabyte Corporation
  1685 38th St.
  Boulder, CO 80301
  
  


______________________________ Reply Separator _________________________________
Subject: Entek Plus Cu-106A
Author:  [log in to unmask] at UNIXMAIL
Date:    1/10/97 12:41 AM


Dear All:

Our customer is asking us how to implement no-clean assembly process on
Entek Plus Cu-106A from Enthone.Our customer's product is 2 side SMT/BGA
without lead component. Is there anyone help us to get below answer.

1.What kind of no-clean solder paste is most compatible to Cu-106A ?
2.What will the max. storgae time after open bag to assembly? Is there
any concern to store in controlled environment ?
3.Is it necessary to reflow in Nitrogen environment ?
4.What is the max. hold time between first and second IR reflow ?
5.How to rework bad paste printing like skip or misalignment ? 
6.Any other concern using Cu-106 A?

Your input will be highly appreciated.

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