Does the bare copper (before soldermask) fail with the one vendor's 
     laminate and not the after soldermask test?
     
     Here are a couple more things that can effect SIR. 
     
     
     The laminate from different vendors can effect the SIR values. Some of 
     the reasons are:
     
     1) The thickness of the resin on top of the glass weave is important. 
     Too little resin on top of the glass especially in a bifluoride solder 
     strip, (which will attack the resin) could yield areas where there is 
     no resin protecting the glass. The plating chemisties can now filter 
     through the exposed lateral glass bundles and cause SIR problems. The 
     after soldermask panel processed at the same time with the same 
     material could actually be higher than the bare copper values.
     
     2) Does the laminate Vendor use the same build and material for the 
     SIR laminate? A higher resin glass weave would be better than a low 
     resin glass weave. 
     
        Is the material difunctional, multifunctional, or tetrafunctional.
     
     3) Different laminate suppliers may have different copper foil 
     suppliers. The copper foil could have different amounts of chromate  
     or zinc.
     
        Sailine can be found in and around the foil. This is a metal 
     chelator. Excessive amounts can result in the tin or tin/lead in the 
     solderstrip chemistry to attach to the sailine.  
     
        What type of solder strip chemistry is used. (nitric or ammonium 
     bifluoride? In nitric the tin/lead is more soiluble and in the 
     bifluoride the tin is more soluable.
     
      
     
       To help narrow down what could be the cause and the list is long. 
     
     Take a cross section of a known good and bad comb. Look at the 
     conductor widths, the glass structure the resin on top of the glass to 
     see if any noticeable differences can be found.
     
     evaluate the comb areas of a good and bad board under a microscope.
     
     When doing the SIR testing, take readings before humidity and after 
     humidity is applied. If the failure mechanism is metal spots the 
     values should be similar. If the failure is due to salts or organics 
     the readings before humidity should be much higher than after humidity 
     is applied.
     
     Compare the SIR values to any Ionic Cointaimnation testing that is 
     done. A high run for ionic testing may give a clue as to the nature of 
     the problem.
     
     Ensure that the SIR panels are carefully handled and that they are 
     processed the same.
     
     Steve Zimmer
     
     Hadco 
     
      
     
     
______________________________ Reply Separator _________________________________
Subject: Re: IONIC TESTING
Author:  [log in to unmask] at SMTPLINK-HADCO 
Date:    7/10/97 08:48 AM
     
     
Rudy, You are SO right !!  As we all discover at some point in our lives, 
"you really do get what you pay for" ....  I'm having a difficult time 
trying to justify to Purchasing that just becuase a laminate manufacturer or 
(worse yet) distributor says his material meets say Mil-S-13949/4, that 
doesn't mean we can indiscriminately "drop" it into out processing line and 
not expect anything to change!!  
     
     
At 10:54 PM 7/9/97 -0400, you wrote:
>In a message dated 97-07-09 05:27:25 EDT, you write: 
>
>>Having seen lots of SIR data from OTHER facilities, the problem could be a 
>>fault in the tester, or technique.  Did good old Bob retire around that 
>time?
>> Did water quality in the rinse system change?  Did the DI water unit 
>>suddenly go south?  There are lots of factors that can cause poor SIR. 
> Don't
>>assume any one factor is the problem.  
>
>Sir Doctor Guru of SIR
>
>You run two pieces of laminate, one from vendor A, the other from vendor B, 
>through the same process, and one passes easily, the other fails miserably, 
>and you repeat this test, with 100% reproducability.... if you can make 
>another deduction from this data, TechNet is awaiting your assessment....:-) 
>>
>>I do agree that no two laminates are the same.  Varying levels of porosity 
>>and varying resin compositions can dramatically effect SIR, or at least 
>their
>>processing characteristics.
>>
>Sir Doctor:
>
>Most of the poor, overstressed PCB fabricators have only their vendors to 
>(pick one) 1. turn to for assistance  2. blame, and having been in both 
>positions more than once, it is clear to me that we all need to see what the 
>options are.   I for one, and suspect many others, never considered that 
>laminate could vary to this extent.   This was a great learning experience 
>for me, and I was hoping to spread the benefits....
>
>Yours in science, and PCB fabrication: 
>
>Rudy Sedlak
>RD Chemical
>
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