Good response.  This accurately reflects my opinion on the 
subject also.

Bruce Wooldridge
DSC Communications Inc.
Plano, Texas
______________________________ Reply Separator _________________________________
Subject: Delamination/response
Author:  [log in to unmask] at SMTPLINK
Date:    10/15/95 01:54 PM


Response to Jerry Cupples:

Nice part about this forum is that we can have a difference of 
opinion that's not considered an argument.  As this discussion has 
become so long, I'm going to start over over again.  The following 
should summarize most of this discussion.

This discussion began with the following statement from Mike Cussen:

"I ran into a delamination problem with an individual supplier on (2) 
different multilayer boards (FR-4) after the IR process in our SMT 
assembly.

My question is:  "Is it necessary to bake the blank boards prior to 
the SMT process and if so, what are some of the guidelines I may use. 
"

I'm not sure if it was Mike Cussen or someone else that stated that a 
vendor requested a bake cycle of the bare-boards prior to IR reflow.  
However, I am sure that it is recommended by IPC.

Response to Jerry:

We both agree that baking boards diminishes solderability.  We also 
agree that delamination problems are seldom an issue when not baking. 
 We both agree that today's boards should not require baking prior to 
any soldering operation to prevent delamination.  However, we are at 
issue on liability and who is responsible when not baking.

You stated that when a vendor insists on baking prior to IR reflow, 
you would no longer do business with that vendor.  Well Jerry, your 
present vendor (first-class people represented here) has nothing to 
worry about because you already bake your boards at 110 degrees "C" 
for a minimum of (4) hours (and usually overnight).  I only refer to 
your vendor as "first-class" as this is how you stated it.  You infer 
that anyone that insists that you bake may not be first-class.

Though I agree baking may not be necessary, it is an added insurance 
factor against delamination.  When boards go through the HASL process 
at your vendors plant, they are submerged in 465 degree "F" solder for 
5 to 6 seconds.  This is an excellent thermal stress (not thermal 
shock) test.  If delamination was going to happen, it should show up 
here.  However, it must be remembered that vendor always bakes the 
boards just prior to the HASL process. When you mass solder your 
boards in an IR oven, they are in the tunnel for a lot longer than 5 
to 6 seconds.  Therefore, when a vendor requests a bake cycle before 
your IR, just as they have done before HASL, I don't feel this to be 
an unreasonable requirement.  Of course, no one can force you to bake.
  However, who does the liability belong to?

When you bake boards, 10 - 20 in a stack, it must be assumed that 
baking is done before the assembly of components.  This infers that 
there is a reasonable time frame between baking and soldering.  This 
also infers that the only accomplishment in this case would be 
diminishment of solderability.  When baking boards in a stack, it 
would require considerable for the boards in the middle of the stack 
to come up to temperature.  In addition, where does the moisture go 
when stacking?  To the next board in the Stack???  Whenever baking 
boards, they must be separated to allow them to rapidly come up to 
temperature, with free air flow around each individual board, to 
allow any moisture to dissipate.  This only makes good common sense.  
When baking populated, or unpopulated, they must always be separated 
when in the oven.

Baking will only serve its intended purpose, if done within 3 to 4 
hours just prior to any soldering process.  Otherwise, it is a wasted 
effort.  All board material has very high moisture absorbtion 
properties - some more than others.  Let's assume that you bake all 
of the moisture out of your boards and then return them to your store 
room or assembly area.  All of the moisture in the specific 
environment will be absorbed back into the board material in much 
less than 24 hours.  If your environment is 30% RH, then this will 
represent the moisture factor.  If it is 70% RH, then this would be 
the moisture factor.  If you store them in a bucket of water, this 
would be the moisture factor, etc., etc., etc..  A simple weight loss 
test can be performed to determine exact moisture factors.

You stated in your earlier response that you have an agreement with 
your first-class vendor to eat your components when failures occur.  
In today's business climate, many vendors do this either to win your 
business or hold your business.  You stated that you have only 
returned one or two boards about six times over the past few years.  
If this is the case, your present vendor has made a pretty good 
business decision.  Not too many dollars lost!  However, though the 
vendor is eating a limited number of boards with components, what do 
you think the response would be with 100 - 200 boards, six times over 
the past few years.  My money would go on them dropping you as a 
customer after the 2nd or 3rd time.  Just wait until the industry 
gets busier and deliveries get extended to 12 to 16 weeks (and it's 
coming).  My money must again go to no one eating your components.  
After all, why should they?  It requires over 100 processes to 
manufacture a multilayer board.  Though an attempts is made to 
control all of the processes, by all first-class vendors, #%&@ does 
happen from time to time.  There is absolutely no way that a vendor 
can 100% guarantee the quality, 100% of the time.  Even with 
destructive testing on every board, there is no 100% guarantee.  
Therefore, shared liability.  The bare-board to the vendor,... the 
components to the user.

You suggested that the delamination problem may have been the 
material.  Why then would the vendor not go back to the material 
supplier and make them pay for your loss, plus the cost of the board? 
 Becausethe laminate supplier will only give a credit for the cost of 
raw material and nothing else!

I would like to know what the term partnership truly means.  It's a 
nice term and sounds pretty good.  We all would like to think that we 
are good partners.  Watch the partnership vanish when the quote 
reaches your purchasing department.  Does your agreement with your 
vendor to eat components include a partnership?  Is this agreement 
with your top name vendor, with impeccable abilities (the way you put 
it) in writing?  It should be!  If it is in writing, I sure would 
like to see a copy.  Does this vendor give all of his customers the 
same agreement, or do they only consider some of their customers good 
enough for this agreement?  Those that don't have the same agreement 
must suffer the burden of the loss of your components.

With all of this in mind, what is wrong with a simple bake cycle when 
it is requested or insisted upon?  This is nothing more than what the 
vendor does in their own process prior to HASL.  I'm sure that the 
laminate supplier imposes the same requirement on your vendor.   At a 
minimum, it is an added insurance policy to help prevent delamination.
  Though we both agree that baking is not necessary, it is only I 
that would be willing to to accept the consequences for not following 
the vendors requirements. 

As you stated, baking boards is not a cure-all.  However, it is an 
insurance policy agianst delamination of a product that must face 
extreme temperature during processing.  It also eliminates a contest 
that may arrive from delemaination from vendors requiring baking.  
And it's not a big deal!

Sorry that this was so lengthy.  This would be an excellent subject 
for a debate.  This is my last response on this subject.

Norm Einarson
PRINTED CIRCUIT TECHNOLOGY
(by the way, I'm not a vendor)