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Thread

Bonding copper to FR4 core material

2012-08-15 by Dave M

I've followed a thread on the Tekscopes group for several days, hoping that 
someone would ask the question that's eluded me for years.  My question is 
in regard to the raw PCB manufacturing process; hopefully, someone can 
provide a clue.

My question is: what process is used to prepare the surface of the copper 
sheet prior to bonding to the bare fiberglass (e.g., FR4) board?  If you've 
ever lifted a trace from a PCB, you've probably noticed that the copper 
surface that was bonded to the fiberglass board had some kind of brownish 
coating on it.  Logic would lead one to think that this coating would help 
the copper to securely bond to the fiberglass.

I've noticed that on some boards, the copper-fiberglass bond is quite 
tenacious, requiring a good bit of effort to break it.  Applying heat and 
pressure is the easiest method, but physically pulling a copper trace form 
the board can be difficult if you're trying to salvage the trace.

I would like to know how the copper sheet is prepared prior to bonding to 
the board.  Anyone know?

Cheers,
Dave M 


[Non-text portions of this message have been removed]

Re: [Homebrew_PCBs] Bonding copper to FR4 core material

2012-08-16 by John Anhalt

See page 26 and 27 here: http://www.jjorly.com/g10_fr4_sheets_fabricator.htm  Most copper is electrodeposited (i.e., plated) onto the FR4.

John

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  ----- Original Message ----- 
  From: Dave M 
  To: Yahoo Homebrew_PCB 
  Sent: Wednesday, August 15, 2012 7:28 PM
  Subject: [Homebrew_PCBs] Bonding copper to FR4 core material

  I've followed a thread on the Tekscopes group for several days, hoping that 
  someone would ask the question that's eluded me for years. My question is 
  in regard to the raw PCB manufacturing process; hopefully, someone can 
  provide a clue.

  My question is: what process is used to prepare the surface of the copper 
  sheet prior to bonding to the bare fiberglass (e.g., FR4) board? If you've 
  ever lifted a trace from a PCB, you've probably noticed that the copper 
  surface that was bonded to the fiberglass board had some kind of brownish 
  coating on it. Logic would lead one to think that this coating would help 
  the copper to securely bond to the fiberglass.

  I've noticed that on some boards, the copper-fiberglass bond is quite 
  tenacious, requiring a good bit of effort to break it. Applying heat and 
  pressure is the easiest method, but physically pulling a copper trace form 
  the board can be difficult if you're trying to salvage the trace.

  I would like to know how the copper sheet is prepared prior to bonding to 
  the board. Anyone know?

  Cheers,
  Dave M 

  [Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Re: Bonding copper to FR4 core material

2012-08-16 by David

--- In Homebrew_PCBs@yahoogroups.com, "John Anhalt" <janhalt@...> wrote:
>
> See page 26 and 27 here: http://www.jjorly.com/g10_fr4_sheets_fabricator.htm  Most copper is electrodeposited (i.e., plated) onto the FR4.
> 
> John

> 
>   I would like to know how the copper sheet is prepared prior to bonding to 
>   the board. Anyone know?
> 
>   Cheers,
>   Dave M 
> 

Thanks, John, but that link leads me only to marketing pages.  I haven't been able to find any documents containing 27 or more pages.  Can you point me to a link to the actual document to which you were refering?

My further research leads me to understand that the copper isn't electrodeposited directly onto the core material, but is electrodeposited onto a stainless steel cylinder or drum, which is then bonded onto the uncured epoxy core.  Shiny copper won't bond very well with epoxy, so I logically deduce that the copper must be treated in some way before bonding.

My question remains, how is the copper sheet treated before bonding?  Acid etch? 
Also, the epoxy used to make the base material seems to be more heat resistant than the common repair epoxy found in hardware stores. What kind of expoy is used to make the core material?  Is it available to me as a consumer?

Cheers,
Dave M

Re: [Homebrew_PCBs] Re: Bonding copper to FR4 core material

2012-08-16 by Les Newell

If I remember correctly the copper is oxidized first. The oxide forms a 
a slightly porous structure that allows a good bond. Layers of woven 
glass cloth are impreganted with epoxy then laminated up with the 
copper. The whole lot is then compressed and heated to cure the epoxy.

High temperature cure epoxy is much stronger and more heat resistant 
than the cheap two part room temperature stuff you get in a local 
hardware store.

Les

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On 16/08/2012 15:34, David wrote:
>
>
> Thanks, John, but that link leads me only to marketing pages.  I haven't been able to find any documents containing 27 or more pages.  Can you point me to a link to the actual document to which you were refering?
>
> My further research leads me to understand that the copper isn't electrodeposited directly onto the core material, but is electrodeposited onto a stainless steel cylinder or drum, which is then bonded onto the uncured epoxy core.  Shiny copper won't bond very well with epoxy, so I logically deduce that the copper must be treated in some way before bonding.
>
> My question remains, how is the copper sheet treated before bonding?  Acid etch?
> Also, the epoxy used to make the base material seems to be more heat resistant than the common repair epoxy found in hardware stores. What kind of expoy is used to make the core material?  Is it available to me as a consumer?
>
> Cheers,
> Dave M
>
>

Re: Bonding copper to FR4 core material

2012-08-16 by twb8899

The copper foil used for printed wiring laminates is treated on one side with an oxide coating. This oxide coating gives the copper surface a crystalline texture for adhesion to the glass epoxy bonding sheets and laminate. The foil is bonded under heat and pressure using B stage bonding sheets. 

It goes like this:

Oxide treated copper foil with the oxide side facing down

B-stage prepreg bonding sheet(s)

C-stage laminate


B stage prepreg is epoxy impregnated glass cloth that is cured until "tack free" but not fully cured. It will flow out and bond the layers under heat and pressure. 

C stage is fully cured laminate such as FR-4 etc. that is commonly used.

There are many types of prepreg materials available with various resin and glass makeups. There are also many types of oxides available. Black, brown and red oxides are widely used. 

I used brown oxides when I made multilayer boards due to the finer crystalline structure. The foil had a brown oxide coating as well. Sometimes you can see the oxide coating inside of a multilayer board. It's easiest to spot on larger internal ground planes. That's why the internal copper layers will often look darker and not a copper color. 

Tom

--- In Homebrew_PCBs@yahoogroups.com, "Dave M" <dgminala@...> wrote:

Show quoted textHide quoted text

>
> I've followed a thread on the Tekscopes group for several days, hoping that 
> someone would ask the question that's eluded me for years.  My question is 
> in regard to the raw PCB manufacturing process; hopefully, someone can 
> provide a clue.
> 
> My question is: what process is used to prepare the surface of the copper 
> sheet prior to bonding to the bare fiberglass (e.g., FR4) board?  If you've 
> ever lifted a trace from a PCB, you've probably noticed that the copper 
> surface that was bonded to the fiberglass board had some kind of brownish 
> coating on it.  Logic would lead one to think that this coating would help 
> the copper to securely bond to the fiberglass.
> 
> I've noticed that on some boards, the copper-fiberglass bond is quite 
> tenacious, requiring a good bit of effort to break it.  Applying heat and 
> pressure is the easiest method, but physically pulling a copper trace form 
> the board can be difficult if you're trying to salvage the trace.
> 
> I would like to know how the copper sheet is prepared prior to bonding to 
> the board.  Anyone know?
> 
> Cheers,
> Dave M 
> 
> 
> [Non-text portions of this message have been removed]
>

Re: Bonding copper to FR4 core material

2012-08-17 by David

Many thanks for that insight, Tom.  I'm interested in knowing this technique and processesz involved in order to create more permanent  PCB repairs.  I've used the common 2-part hardware store variety epoxy for years, but have always been less than satisfied with the outcome; the main reason being the sensitivity of the epoxy to soldering heaat and the lack of a significant bond between the copper and the epoxy. 
I figured that if I could prepare the bottom surface of the new copper trace(s), and find the right high temperature epoxy, then my repairs would be more professional and permanent.
Thanks again for the info.
Now, the question is; where might I find the various oxide treatment chemicals and high temperature epoxy?
I'll continue searching, of course (now that I have a bit more knowledge than before), but a point in the right direction  (manufacturers names, chemical names, etc.) would save time.

Many thanks!!!
Dave M


--- In Homebrew_PCBs@yahoogroups.com, "twb8899" <twb8899@...> wrote:

Show quoted textHide quoted text

>
> The copper foil used for printed wiring laminates is treated on one side with an oxide coating. This oxide coating gives the copper surface a crystalline texture for adhesion to the glass epoxy bonding sheets and laminate. The foil is bonded under heat and pressure using B stage bonding sheets. 
> 
> It goes like this:
> 
> Oxide treated copper foil with the oxide side facing down
> 
> B-stage prepreg bonding sheet(s)
> 
> C-stage laminate
> 
> 
> B stage prepreg is epoxy impregnated glass cloth that is cured until "tack free" but not fully cured. It will flow out and bond the layers under heat and pressure. 
> 
> C stage is fully cured laminate such as FR-4 etc. that is commonly used.
> 
> There are many types of prepreg materials available with various resin and glass makeups. There are also many types of oxides available. Black, brown and red oxides are widely used. 
> 
> I used brown oxides when I made multilayer boards due to the finer crystalline structure. The foil had a brown oxide coating as well. Sometimes you can see the oxide coating inside of a multilayer board. It's easiest to spot on larger internal ground planes. That's why the internal copper layers will often look darker and not a copper color. 
> 
> Tom
> 
> --- In Homebrew_PCBs@yahoogroups.com, "Dave M" <dgminala@> wrote:
> >
> > I've followed a thread on the Tekscopes group for several days, hoping that 
> > someone would ask the question that's eluded me for years.  My question is 
> > in regard to the raw PCB manufacturing process; hopefully, someone can 
> > provide a clue.
> > 
> > My question is: what process is used to prepare the surface of the copper 
> > sheet prior to bonding to the bare fiberglass (e.g., FR4) board?  If you've 
> > ever lifted a trace from a PCB, you've probably noticed that the copper 
> > surface that was bonded to the fiberglass board had some kind of brownish 
> > coating on it.  Logic would lead one to think that this coating would help 
> > the copper to securely bond to the fiberglass.
> > 
> > I've noticed that on some boards, the copper-fiberglass bond is quite 
> > tenacious, requiring a good bit of effort to break it.  Applying heat and 
> > pressure is the easiest method, but physically pulling a copper trace form 
> > the board can be difficult if you're trying to salvage the trace.
> > 
> > I would like to know how the copper sheet is prepared prior to bonding to 
> > the board.  Anyone know?
> > 
> > Cheers,
> > Dave M 
> >