Homebrew PCBs

I saw a process used by a fab house and they used a negative photo 
resist and then tin coated the board.  The tin only stuck to the 
places that had the bare copper.  Then the board was chemically etched 
and the tin protects the copper.  Would we possibly be able to come up 
with a similar system of printing a negative image and then tin 
plating before etching?  The toner would probably melt when you tried 
to tin the board with an iron, but maybe a chemical plating process?

Does anyone know for sure if tin etches away with FeCl?  I might have 
to try it at lunch...haha.

matt

On Mon, 27 Mar 2006 17:50:06 +0200, matt clement <buckeyes1997@...>  
wrote:

> I saw a process used by a fab house and they used a negative photo
>
> resist and then tin coated the board.  The tin only stuck to the
>
> places that had the bare copper.  Then the board was chemically etched
>
> and the tin protects the copper.  Would we possibly be able to come up
>
> with a similar system of printing a negative image and then tin
>
> plating before etching?  The toner would probably melt when you tried
>
> to tin the board with an iron, but maybe a chemical plating process?
>
>
> Does anyone know for sure if tin etches away with FeCl?  I might have
>
> to try it at lunch...haha.
>
>
> matt
>


I'm not sure about FeCl, those tin resist baths are usually Sulphuric acid  
/ peroxyde i think.
You could do things that way, but why do you want to?

ST

It is my understanding you tin plate the pcb after etching to 
protect the new copper trace from corrosion. TINNIT is the name of 
the material used to tin plate.

--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
<stefan_trethan@...> wrote:
>
> On Mon, 27 Mar 2006 17:50:06 +0200, matt clement 
<buckeyes1997@...>  
> wrote:
> 
> > I saw a process used by a fab house and they used a negative 
photo
> >
> > resist and then tin coated the board.  The tin only stuck to the
> >
> > places that had the bare copper.  Then the board was chemically 
etched
> >
> > and the tin protects the copper.  Would we possibly be able to 
come up
> >
> > with a similar system of printing a negative image and then tin
> >
> > plating before etching?  The toner would probably melt when you 
tried
> >
> > to tin the board with an iron, but maybe a chemical plating 
process?
> >
> >
> > Does anyone know for sure if tin etches away with FeCl?  I might 
have
> >
> > to try it at lunch...haha.
> >
> >
> > matt
> >
> 
> 
> I'm not sure about FeCl, those tin resist baths are usually 
Sulphuric acid  

> / peroxyde i think.
> You could do things that way, but why do you want to?
> 
> ST
>

On 3/27/06, aggie_672000 <aggie_672000@...> wrote:
> It is my understanding you tin plate the pcb after etching to
> protect the new copper trace from corrosion. TINNIT is the name of
> the material used to tin plate.

That's all true.  But I know I read the same thing that Matt did
(where did you see it, Matt?), that some commercial processes use tin
plate as an etch mask.  I don't remember why they did that.

Seems one could do that as a homebrew process:
1. Put toner or leave photoresist where you want to etch
2. Tin plate the areas you want to keep (TINNIT)
3. Remove the toner or photoresist
4. Etch

but I don't see what advantage that would have over the more common
homebrew processes.

Cheers,
- Jan

>
> --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
> <stefan_trethan@...> wrote:
> >
> > On Mon, 27 Mar 2006 17:50:06 +0200, matt clement
> <buckeyes1997@...>
> > wrote:
> >
> > > I saw a process used by a fab house and they used a negative
> photo
> > >
> > > resist and then tin coated the board.  The tin only stuck to the
> > >
> > > places that had the bare copper.  Then the board was chemically
> etched
> > >
> > > and the tin protects the copper.  Would we possibly be able to
> come up
> > >
> > > with a similar system of printing a negative image and then tin
> > >
> > > plating before etching?  The toner would probably melt when you
> tried
> > >
> > > to tin the board with an iron, but maybe a chemical plating
> process?
> > >
> > >
> > > Does anyone know for sure if tin etches away with FeCl?  I might
> have
> > >
> > > to try it at lunch...haha.
> > >
> > >
> > > matt
> > >
> >
> >
> > I'm not sure about FeCl, those tin resist baths are usually
> Sulphuric acid
> > / peroxyde i think.
> > You could do things that way, but why do you want to?
> >
> > ST

Hi,

I am currently starting to make my first PCBs and would like to make my 
own Eagle library to work with (mainly for photo-etch boards and hand 
soldering) because the build in one is not easy to work with. I am full 
of questions now as this is the first time I really need to go into 
detail about packages and solder pads.


What is a good source to find information about the solder pads required 
for the most common packages? It is quite easy to find for e.g. SO8 and 
stuff, but the info on 0603, 0805, and 1206 resistors and SMT and 
through hole capacitors is harder to find. The only thing I could find 
for resistors was here: http://www.mouser.com/catalog/625/478.pdf and 
these pads are way smaller then the ones in the default Eagle libraries.

About capacitors. Are there default sizes as with resistors? I can't 
seem to find a list of available capacitor packages. I've also looked 
for through hole capacitors and there seems to be a lot of difference in 
packaging to.

I've been told that SO8 from one manufacturer is not the same as from 
another one. Don't these kind of packages have default sizes then?

About SMT resistors again. The 0603 etc give a clue about the size in 
hundredths of inches, but most information I find on the net is in 
metric measurements. Are the 0603 packages rounded to 1.6mm x 0.81mm 
these days or are there two kinds of 0603 resistors around?


About through hole pad sizes. I've read somewhere that for through hole 
components a drill size of 0.8mm is recommended, with a round copper pad 
of (at least) 1.3mm. Is that big enough for hand soldering? Why would I 
choose a round pad above a octagonal shaped one? Some documents advice 
to use oval pads for DIP packages, is that true and why is that?


Of course all other information you think might be interesting for me is 
welcome to. Let me also note there is another yahoo group called 
"EagleSVN" that had the intention of creating an Eagle library. It isn't 
really active at the moment, but I hope to contribute some of my 
libraries soon. Those interested in helping us out, please feel free to 
join the group.


Anyways, thanks a lot in advance.



greetings,

Ronald

----- Original Message ----- 

From: "Ronald Vanschoren" <yahoogroups@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Tuesday, March 28, 2006 7:53 AM
Subject: [Homebrew_PCBs] Solder Pads and other questions


> Hi,
>
> I am currently starting to make my first PCBs and would like to make my
> own Eagle library to work with (mainly for photo-etch boards and hand
> soldering) because the build in one is not easy to work with. I am full
> of questions now as this is the first time I really need to go into
> detail about packages and solder pads.
>
>
> What is a good source to find information about the solder pads required
> for the most common packages? It is quite easy to find for e.g. SO8 and
> stuff, but the info on 0603, 0805, and 1206 resistors and SMT and
> through hole capacitors is harder to find. The only thing I could find
> for resistors was here: http://www.mouser.com/catalog/625/478.pdf and
> these pads are way smaller then the ones in the default Eagle libraries.

http://www.ipc.org/

These footprints are for reflow soldering. For hand soldering it's a good 
idea to make the pads longer.

>
> About capacitors. Are there default sizes as with resistors? I can't
> seem to find a list of available capacitor packages. I've also looked
> for through hole capacitors and there seems to be a lot of difference in
> packaging to.

0.1" and 0.2" covers most of the ceramic ones I use.

>
> I've been told that SO8 from one manufacturer is not the same as from
> another one. Don't these kind of packages have default sizes then?
>
> About SMT resistors again. The 0603 etc give a clue about the size in
> hundredths of inches, but most information I find on the net is in
> metric measurements. Are the 0603 packages rounded to 1.6mm x 0.81mm
> these days or are there two kinds of 0603 resistors around?

They are all the same size.

>
>
> About through hole pad sizes. I've read somewhere that for through hole
> components a drill size of 0.8mm is recommended, with a round copper pad
> of (at least) 1.3mm. Is that big enough for hand soldering? Why would I
> choose a round pad above a octagonal shaped one? Some documents advice
> to use oval pads for DIP packages, is that true and why is that?
>

0.8 mm or 0.7 mm are fine for IC pins and sockets. I use 0.7 mm and 0.6 mm 
for vias. Pads should be bigger for single-sided boards than for PTH. Also, 
hand drilling isn't very accurate and a larger pad than usd for CNC drilling 
is advisable. I often add teardrops to pads to make things easier.

Oval pads for ICs make it easier to put a track between them.

Leon
--
Leon Heller, G1HSM
leon.heller@...
http://www.geocities.com/leon_heller

The pc house that I wourked at for a while did tin plate before
etching and then use and ammonia based ecthant.  The process is to
drill, plate the thru holes, tin plate the pattern and then etch.

I tried using a plated piece of pcb material that I silk printed a
pattern on with fecl and it etched through.  

Russ



--- In Homebrew_PCBs@yahoogroups.com, "Jan Kok" <jan.kok.5y@...> wrote:

>
> On 3/27/06, aggie_672000 <aggie_672000@...> wrote:
> > It is my understanding you tin plate the pcb after etching to
> > protect the new copper trace from corrosion. TINNIT is the name of
> > the material used to tin plate.
> 
> That's all true.  But I know I read the same thing that Matt did
> (where did you see it, Matt?), that some commercial processes use tin
> plate as an etch mask.  I don't remember why they did that.
> 
> Seems one could do that as a homebrew process:
> 1. Put toner or leave photoresist where you want to etch
> 2. Tin plate the areas you want to keep (TINNIT)
> 3. Remove the toner or photoresist
> 4. Etch
> 
> but I don't see what advantage that would have over the more common
> homebrew processes.
> 
> Cheers,
> - Jan
> 
> >
> > --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
> > <stefan_trethan@> wrote:
> > >
> > > On Mon, 27 Mar 2006 17:50:06 +0200, matt clement
> > <buckeyes1997@>
> > > wrote:
> > >
> > > > I saw a process used by a fab house and they used a negative
> > photo
> > > >
> > > > resist and then tin coated the board.  The tin only stuck to the
> > > >
> > > > places that had the bare copper.  Then the board was chemically
> > etched
> > > >
> > > > and the tin protects the copper.  Would we possibly be able to
> > come up
> > > >
> > > > with a similar system of printing a negative image and then tin
> > > >
> > > > plating before etching?  The toner would probably melt when you
> > tried
> > > >
> > > > to tin the board with an iron, but maybe a chemical plating
> > process?
> > > >
> > > >
> > > > Does anyone know for sure if tin etches away with FeCl?  I might
> > have
> > > >
> > > > to try it at lunch...haha.
> > > >
> > > >
> > > > matt
> > > >
> > >
> > >
> > > I'm not sure about FeCl, those tin resist baths are usually
> > Sulphuric acid
> > > / peroxyde i think.
> > > You could do things that way, but why do you want to?
> > >
> > > ST
>

on Tue, 28 Mar 2006 at 04:36, aggie_672000 wrote:
>It is my understanding you tin plate the pcb after etching to
>protect the new copper trace from corrosion. TINNIT is the name of
>the material used to tin plate.

[Please don't top-post]
[Please _do_ trim your quotes]

Your understanding is correct and that is one such product,
which applies a tin coating by purely chemical means..

However, if you had been attendiing to this thread you might
have understood that it is about applying a tin plating as an
etch-resist _before_ etching. This is done through a developed
photo-resist or similar while the copper foil is still intact, so
there is no need to use an electroless plating solution.

After etching, the tin layer may then be chemically stripped.

To go some way towards answering the OPs question...
On Mon, 27 Mar 2006 at17:50 +0200, matt clement  wrote:
>...fab house...used a negative photo resist...then tin coated...board.
>...Then the board was chemically etched... the tin protects the copper.
>Would we...be able to come up with a similar system... printing a
>negative image and then tin plating before etching?

As Stefan says, yes but why bother? Extra work, more
messy chemicals, another hazardous waste problem...

>The toner...probably melt when...tin the board with an iron,
>but maybe a chemical plating process?

If you are already using an electroless tinning process
to protect the finished board you could use that, but
since the copper foil is still intact electroplating is feasible.

>Does anyone know for sure if tin etches away with FeCl?

A visit to Electrochemical Series (Corrosion Reactions) for Common Metals
http://www.efunda.com/materials/corrosion/electrochem_list.cfm?sort=com
suggests that it would - even the high level of copper ions could, but
the picture might be complicated by the low solubility of some tin salts,
by bath additives which exploit this or, if it were a tin/lead coating, by
passivation effects (really another way of saying the same thing).

The commercial process described here implies it does:
http://www.pcbfab.com/outreth2.html
"Etching Outerlayer Printed Circuit Boards"
 >The use of Tin or Tin/Lead as an etch resist essentially mandates
 >the use of ammoniacal etchant, because this is the only commonly
 >used etchant chemistry that will not attack the Tin or Tin/Lead.


Regards, LenW
-- 
   A: Because it destroys the flow of the conversation
   Q: Why is top-posting bad?

Why don't top-post? saves us all a lot os useless scrolling and searching  
for the reply.
If you reply in one paragraph, and not several mixed in with the OP,  
top-posting seems perfectly acceptable (even better) to me and ther is no  
rule against it that i'm aware of.

I'm not sure the tinnit and other electroless stuff would make a thick  
enough plating to work as resist.

ST



On Wed, 29 Mar 2006 02:59:31 +0200, Len Warner <yahoo@...>  
wrote:

> [Please don't top-post]
>
> [Please _do_ trim your quotes]
>
>
> Your understanding is correct and that is one such product,
>
> which applies a tin coating by purely chemical means..
>
>
> However, if you had been attendiing to this thread you might
>
> have understood that it is about applying a tin plating as an
>
> etch-resist _before_ etching. This is done through a developed
>
> photo-resist or similar while the copper foil is still intact, so
>
> there is no need to use an electroless plating solution.
>
>
> After etching, the tin layer may then be chemically stripped.

In a message dated 3/29/2006 2:24:48 A.M. Central Standard Time,  
stefan_trethan@... writes:

I'm not  sure the tinnit and other electroless stuff would make a thick   
enough plating to work as resist.



Correct.


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

JanRwl@... wrote:
>  
> In a message dated 3/29/2006 2:24:48 A.M. Central Standard Time,  
> stefan_trethan@... writes:
> 
> I'm not  sure the tinnit and other electroless stuff would make a thick   
> enough plating to work as resist.
> 
> 
> 
> Correct.
> 

It has not to do with tin plating thickness, but chemical reactivity. 
Tin will react with all acidic copper etchers that I know of. That is 
why anyone who wants to etch a PCB using tin as a metal etch resists 
must use an alkaline based copper etchant. The higher the pH the more 
stable tin metal becomes. A common alkaline etchant is the ammonia 
chloride types used by most of the PCB fabricators in the world.