Eric,
Some other information with respect to acid copper plating. Remember that
there are othjer factors at play such as the action of the organic addition
agents, cathode current densities, ionic migration, etc. that will play a
role in overall plating distribution. Of course cathodic polarization is a
key factor. In addition, polarization ismade up of: (1) Activation
polarization, (2) Concentration polarization and (3) Resistance
polarization. All play a role and understanding the various components and
how each influences plating distribution and throwing power. Over coming the
effects of ohmic resistance is also a key factor in improving throwing
power.
In addition, one should not confuse microthrowing power with macrothrowing
power.
One can easily determine the influences of cathode efficiency by utilizing a
Haring-Blum Cell to study measure cathode efficiency.
Basically, high operating tempertaures, high metal conc, and low acid will
favor the high current density area of any part that is being plated.
-----Original Message-----From: Eric Yakobson
<[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Saturday, October 31, 1998 7:34 PM
Subject: Re: [TN] Copper plating & Copper thickness
>Michael,
>
>With all due respect, I'm afraid I have to disagree with your explanation.
>While it is true that cathode current efficiency for a typical acid copper
>electrolyte is close to 100%, this is exactly the reason why it does not
>have any effect on current distribution. The key to the explanation of
>this phenomenon is cathode polarization (sorry for the electrochemical
>terminology, but it would be rather difficult to explain this without using
>it).
>
>At low average current density the difference between cathode polarization
>on lower/higher current density points of the cathode in most electrolytes
>(including acid copper) is normally much greater than at high average
>current density. Therefore, the current distribution is more uniform at
>low average current density.
>
>In most alkaline electrolytes, where current efficiency is much lower than
>100% (the rest of the current is consumed for hydrogen gas evolution), it
>does affect the current distribution favorably. Since at higher densities
>more current is consumed for hydrogen evolution, the metal distribution
>generally is more uniform then in acid solutions.
>
>Low current density will result in higher throwing power in both systems.
>One of the few practical exceptions to this rule (low current density/high
>throwing power) is hex-chromium electrolyte, in which current efficiency is
>directly proportional to current density.
>
>As to the minimum copper thickness, historically (by trial & error I guess)
>it was determined that 1 mil (25 micron) of copper is a minimum thickness
>that will reliably withstand multiple solder floats. From my practical
>experience, 0.5 mil cracks much more readily, which is understandable,
>considering the fact that copper tensile strength is proportional to the
>thickness of the deposit.
>
>Best regards.
>
>Eric Yakobson
>Alpha PC Fab
>
>
>
>
>
>
>mcarano <[log in to unmask]> on 10/31/98 07:30:36 AM
>
>To: [log in to unmask]
>cc: (bcc: Eric Yakobson/AlphaPCFabUS/Cookson)
>Subject: Re: [TN] Copper plating & Copper thickness
>
>
>
>
>Dear Francis,
>
>The best explanation for any type of electroplating in an acid medium has
>to
>do with plating efficiency. Generally, acid plating process like the acid
>copper, acid tin etc are close to 100% efficient. In other words, the
>plating favors the high current dednsity areas of a pwb(the surface as
>opposed to the hole) By lowering the cathode current density, you now tend
>to favor the low current areas somewhat, and thus improve throwing power.
>This works just the opposite with alkaline based plating solutions.
>
>With respect to high frequency and plating unformity, I am not sure.
>Generally, the more thickness inside the hole, the better the hole wall
>plating is able to stand up to thermal excursions.
>
>Hope this helps.
>
>-----Original Message-----
>From: Francis Lai <[log in to unmask]>
>To: [log in to unmask] <[log in to unmask]>
>Date: Saturday, October 31, 1998 9:30 AM
>Subject: [TN] Copper plating & Copper thickness
>
>
>>Dear Sir :
>>
>>I work inn a high frequency PCB manufacturing company and I have the
>>
>>following questionns :
>>
>>1/ Why is it for copper plating (acid copper plating) the lower the
>> current, the more the throwing power ? If I start to plate copper
>> on the PTH walls with high current density after PTH, what will
>> happen ?
>>
>>2/ Our customer always specify to have a certainn thickness innside the
>> PTH walls for copper. Why is that so for high frequency PCB ?
>> What happen if copper thickness is thinner than the specified
>> thickness at high frequencies ?
>>
>>Thanks for your help !!!!!!!
>>
>>my e-mail : [log in to unmask](this is only text base, pls do not
>send
>> graphics)
>>
>>Thamks again!!!!!!!
>>
>>Francis
>>
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