Re: Dark deposit on pins near leaking SMD electrolytic caps


Chuck Harris <cfharris@...>
 

Back when 2 layer boards were not quite good enough, and 4 layer
boards attached a pretty hefty premium, some, including myself,
made 3 layer boards.

A 4 layer board can be made in a couple of different ways:

1) SS bonded to DS bonded to SS
2) DS bonded to blank bonded to DS

In either case , there are 3 fiberglass layers, and 4 metal layers.

A 3 layer board is made by a SS bonded to a DS.

The 3 layer board has only 2 fiberglass layers, and 3 metal layers.

They work well when the boards are small, but larger sized boards
are bound to be warped from the start.

Other than cost, 3 layer boards work well with TTL circuitry, as
you typically use the middle layer as a ground plane, and salt little
ceramic capacitors to every chip's VCC pin.

-Chuck Harris

Jim Ford wrote:

OK.  I will change my story to I've never seen 3-layer boards.

Usually when I see something that doesn't make sense, I attribute it to "It must have
been less expensive to do it that way."

Thanks, Harvey.

Jim

------ Original Message ------
From: "Harvey White" <madyn@dragonworks.info>
To: TekScopes@groups.io
Sent: 2/9/2021 8:53:30 PM
Subject: Re: [TekScopes] Dark deposit on pins near leaking SMD electrolytic caps

Physically, one layer, copper on top.

inner layer (* see note)

outer layer, copper on bottom.

That inner layer can be single sided or two sided, depending.  I don't think that
anything in the manufacturing process keeps it from being so.  I've actually made 3
layer boards, although they're quite awkward without plated through holes.

One side of that inner layer can be missing, so yes, a 3 layer board.  I guess it
was cheaper to make for some reason, but that was then, long ago (in electron
lives) then...

Harvey


On 2/9/2021 11:33 PM, Jim Ford wrote:
3-layer boards?  Never heard of them.  Maybe you mean 3 dielectric layers and 4
metal layers?  PCBs are built up from the inside out, starting with a core (fully
cured dielectric sheet plated on both sides with copper foil) and adding more
cores and/or prepregs (partially cured dielectric sheet plated on one side with
copper) symmetrically on both sides until the stackup is done.  Hence there is
always an even number of (metal) layers.  Always!

Jim Ford

------ Original Message ------
From: "greenboxmaven via groups.io" <ka2ivy=verizon.net@groups.io>
To: TekScopes@groups.io
Sent: 2/9/2021 6:02:16 PM
Subject: Re: [TekScopes] Dark deposit on pins near leaking SMD electrolytic caps

The Sonys have three layer boards, I didn't have any problems. However, I can
imagine some very bad problems if the electrolyte got into a connection that
connects with one of the inner layers. How would you deal with that?

     Bruce Gentry, KA2IVY


On 2/9/21 20:44, Raymond Domp Frank wrote:
On Wed, Feb 10, 2021 at 02:38 AM, greenboxmaven wrote:

I have restored some Sony video recorders that were loaded with the bad
condensers.
The affected Tek 'scopes use multilayer boards, making a slightly more intricate
procedure advisable.

Raymond






















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