There seems to be a continuing misunderstanding of the forces at work in
plating through holes. First, you're reporting fairly thick copper at the
knee of the hole. The assumption is that the thickness diminishes toward
the center of the hole. If the hole is cross-sectioned do you find this to
be the case? If so, this is normal but not really desirable.
There's more expansion at the knee of the hole (Werner can you weigh in on
this too please?). If the physical properties of the deposit are poor then
there's the likelihood of cracks at the knee.
As for plating thick boards at low current density, the only reason for
doing this is that there's additional time for the electrolyte to better
circulate through the barrel of the hole. Contrary to some popular beliefs,
the holes of circuit boards are NOT low current density areas. The
thickness of the deposit in the hole is less than on the surface of the
board because the hole doesn't see the same circulation of fresh electrolyte
as the surface. Ogden and Tench proved this over 20+ years ago. Numerous
attempts have been made over the years to improve plating solution
circulation through the hole. It becomes more difficult with thick boards
and/or smaller holes.
Sincerely,
Roger Mouton
EIMC - Advanced Plating Technologies
949 481-5194
www.smartcatshield.com
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----- Original Message -----
From: "Lee parker" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, July 24, 2007 5:49 AM
Subject: Re: [TN] Question on plated through holes general
> Ralph
>
> I presented a paper at IPC this spring on the variables which affect the
> copper uniformity in PTHs. You can probably get a copy by contacting Tom
> Newton at IPC.
>
> It is difficult for me to imagine a greater copper thickness causing the
> barrel to become more susceptible to cracks. The thicker the copper the
> lower the stress for a given load and consequently the lower the strain.
> What may be going on is the uniformity of the copper which causes stress
> concentrations and the ductility of the plated copper. As I mathematically
> demonstrated in my paper, the current density used in plating has a strong
> impact on these parameters. The thicker the board the greater the need for
> low current density.
>
> I would ask the supplier to measure the ductility of the plated copper for
> several current densities and draw your own conclusions.
>
> Best regards
>
> Lee
>
> J. Lee Parker, Ph.D.
> JLP Consultants LLC
> 804 779 3389
>
>
> ----- Original Message -----
> From: <[log in to unmask]>
> To: <[log in to unmask]>; <[log in to unmask]>
> Sent: Tuesday, July 24, 2007 9:00 AM
> Subject: RE: [TN] Question on plated through holes general
>
>
> Lee,
>
> Do you also have any inromation about max Cu thickness in the PTH? In
> the recent past we had some cracks and the min was ok but the max showed
> values aroung .045mm. Our supplier said that the crack was caused due to
> too thick copper. The crack location was on the top just below the Cu
> ring.
> Do you or anybody else has a suggestion how to handle or specify this?
>
> Regards
> Ralph
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker
> Sent: Friday, July 20, 2007 10:42 PM
> To: [log in to unmask]
> Subject: Re: [TN] Question on plated through holes general
>
> David
>
> I always advise one mil or more in the PTH. Given the non-uniformity
> often seen in the PTH I would also spec the drill quality and the ratio
> of the copper at the top of the hole and in the center.
>
> Best regards
>
> Lee
>
> J. Lee Parker, Ph.D.
> JLP Consultants LLC
> 804 779 3389
>
>
> ----- Original Message -----
> From: "David Harman" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, July 20, 2007 4:23 PM
> Subject: [TN] Question on plated through holes general
>
>
> I have a quick question and our standard that we have maybe an older
> one. We currently use the ANSI/IPC-A-600 Rev E
>
>
>
>
>
> Page 70 Micro section:
>
>
>
> There is a table describing copper plating thickness min, requirements
>
>
>
>
>
> Class 1
> Class 2 Class 3
>
> Average Min Thickness .020mm (0.0008in) 0.025mm
> (0.001 in) 0.025 mm (0.001 in)
>
>
>
> Minimum this area .0015 mm( .0006 in) 0.020 mm
> (.0008 in) 0.020mm (.0008 in)
>
>
>
>
>
>
>
> Can anyone tell me if this still is a current standards for copper
> plating thickness measurements.
>
>
>
> David Harman
>
>
>
>
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