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May 1998

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Subject:
From:
Joel Fillion <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 12 May 1998 16:26:35 -0700
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Hi Richard,

Interfacial separation can be caused by a number of things.  First of all,
you must identify if the separation is occurring between the electroless
copper and the post or the electroplated copper and the electroless copper.

In case one, some possible causes could be:

1.  If the rinse following your cleaner on the electroless line is not
adequate, you can carry surfactants into your micro-etch creating a
micro-polish.  The polished surface of the interlayer post can not offer
the mechanical interlock of a micr-etched post.  When thermal cycling a
PCB, depending on the cure level of the laminate,  you will introduce
Z-axis expansion.  In the case of under-cured "green" laminate, Z-axis
expansion can be excessive.  Thus, introducing increased stress on the
interfacial bond.

2.  If the aspect ratio is high for the holes that are experiencing
interfacial separation, there may not be adequate turbulence in the process
baths for the chemicals/rinses to do their jobs.  Make sure there is good
mechanical agitation and the rinses are arranged to create a vortex flow in
the tank.  If you are employing counter-flow rinses, from my experience,
the industry standard for flow is 2-3 gallons per minute.

3.  Depending on the mechanism used for electroless copper bonding, the
"catalyst" for the system may not be performing properly.  Check chemical
concentrations and bath lifes.

In case 2:

1.  From my experience, the main cause for post separation where
electrolytic copper separates from the electroless is high organic levels
in the acid copper bath.  Check for total organic content.  Contact your
chemical vendor for recommended organic levels.  From memory, I believe
anything above 1000 ppm can cause problems. If this is the case, organics
can easily be removed by "carbon treating".

There are other possibilities, but I think I covered the main ones.

I hope this helps,

Joel Fillion
Process Engineer
Matsushita Electronic Materials



 At 10:43 AM 5/12/98 -0400, Richard W. Boerdner wrote:
>howdy folks!
>
>can anyone explain the possible causes in a manufacturing process that
>would result in interfacial separation after thermal stressing of a PCB?
>the temperature profile parameters are -40 C to +55 C with a 6 degree
>per minute rate of rise and an hour dwell time at each extreme for a
>period of 12 hours. the laminate has a glass transition temperature
>rating of 170-180.
>
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