The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: firstname.lastname@example.org (Bob Wilson)
Subject: Re: Multilayer PCB:s, HOW?
Date: Thu, 19 Sep 2002 04:29:22 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
In article , email@example.com says...
>"Roger Johansson" wrote in message
>> I have never worked with multilayer boards, and it just struck me
>> that it is a bit mysterious, how they make such boards.
>> If I imagine a 4-layer board, with +V and ground on the inner planes,
>> then it is impossible to use through holes unless you want to short at
>> least the two middle layers.
>> There is no way to etch these inner layers.
>> So these planes must be etched before the layers are put together.
>> It is topologically impossible to use two middle layers which cover
>> the whole area.
>> But multilayer boards look like the are moulded in one piece, so I
>> have never before imagined that they are created by gluing
>> ready-etched layers together.
>> But that is the only way I can imagine that it works.
>> Maybe I have missed something?
>> How do you create such multilayer boards?
>> And how can you be sure that a pin in a through hole makes contact
>> with a layer of copper it can only see as a very thin ring of copper
>> inside a hole?
>Multilayer boards are made as multiple pairs of thin double-sided boards
>which are eventually sandwiched with thin (not necessarily equally thin)
>layer of partially cured board material, and the whole thing cured as a
>After you'd got to this point you drill out the via holes, and use
>electroless plating to put a thin "seed" layer of platinum (?)
Actually, its palladium. Initiated by an initial stannous deposition.
The palladium acts as a catalyst to initiate the autocatalytic deposition of
the electroless copper. Almost none is required (there is certainly not even
a contiguous layer of palladium to begin the process of electroless
deposition). Copper starts depositing at the sites of palladium, and
continues autocatalytically until the copper sites grow into a contiguous
layer. When sufficient copper is depositied to achieve a very thin
contiguous layer, the drilled laminate is transferred to a copper
electroplating bath that builds up the full layer of copper in the holes.
This is because electroless plating is a very VERY slow process, and is let
go only as long as needed to get full copper coverage. After that much
faster electropating is used to speed up things.
>sides of the via holes, which are then plated up with a couple of microns
>copper. where the drill as gone through copper on one of the inner layers,
>the copper is smeared out around the drill hole and makes reliable contact
>with the plated via.
>This is all second-hand, but I think it is right. For loads of extra money
>you can get "blind vias" whch don't go all the way through the board. I've
>no idea how they do that - I'd guess that they glue the boards together in
>stages and drill and plate the blind vias in the sub-stacks, one sub-stack
>at a time.
>We've got a couple of regulars who are in the business of making printed
>circuit boards, and I'm half hoping to be corrected ...
>Bill Sloman, Nijmegen
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup