By PTH reliability - do you mean properties of the copper eyelet - shock, cyclic stress, or inner layer separation? Or, do you mean coverage, blow-holes and assembly related properties of the through hole?
You have very good answers already about the copper properties. At one time, as Brian points out, there was indication that different "layers" in the copper would stop corner cracks from becoming open circuits. However, if you have to depend on plating layers from copper pyrophosphate and copper sulfate, you don't have a very robust PCB process.
However, if you are only plating 0.5 to 0.6 microns of electroless copper, you do not have much leeway in the microetch step in your cleaning process for pattern plate. If you microetch 0.2 or 0.3 microns in pattern plate cleaning, you may be depending on a very marginal coverage of electroless copper to propagate the main copper pattern electroplate. Do you ever have peeling copper pattern plate, because you cannot microetch enough in the cleaning line after dry film imaging?
Do you have small, high aspect ratio holes where rinse of microetch might become critical? Historically, shops went to "high build" electroless copper of 2.5 microns in the 1980's. The thickness of electroless has been coming down ever since, but you need good, reproducible process control to run at 0.5 microns.
Denny Fritz
-----Original Message-----
From: Brian Ellis <[log in to unmask]>
To: TechNet <[log in to unmask]>
Sent: Tue, Nov 2, 2010 9:23 am
Subject: Re: [TN] Query on Copper plating
I forget the details as this was going back to about 1970 but, in a
ormer life, we did just this kind of thing to reduce barrel cracking.
owever, if I remember rightly, the electrolytic flash coating was only
bout 5 µm. I forget which order they came in but the flash coating and
he 20 µm main plating were done in different baths, one being sulphate
nd the other pyrophosphate. The theory behind it is that the main
lating had a better throwing power, while the flash coating had a
etter adhesion to the electroless copper, because of epitaxial growth.
Again, if my memory serves me correctly, we used this technology for
nly a short while, perhaps 12 months, after which it was replaced by a
ingle bath which had sufficient quality in both aspects to no longer
ustify the extra step. Remember that this was in the relatively early
ays of through hole plating, and finding the right solution (no pun
ntended) was quite an adventure.
I see no justification for doing this today – copper plating has come a
ong way in 40 years!
Brian
On 02/11/2010 06:16, Uppina Nagaraj wrote:
Hi All,
We have a low build electroless Copper plating for Through Hole
metalization, which's giving around 0.5 to 0.6microns of Copper.
The subsequent processes are pattern image printing followed by
pattern plating (electrolytic copper plating).
One of our customer has a requirement to do flash Copper plating
(electro plating) of around 8 to 10 microns, immediately after
electroless Copper plating, prior to pattern image printing.
I want some inputs on the above.....
Is there a distinct advantage on PTH reliability by having
8-10microns of electroplated copper immediately after
electroless Copper plating.
Will having additional flash plating have better Thermal
stress& Thermal Shock performance.
Thanks!
U.Nagaraj
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