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double sided PCB, accuracy

double sided PCB, accuracy

2008-07-04 by Michel Baguet

hi guys,

I got to the point where I can etch 6 mils traces and 32 mils vias with a 12 mils hole with inkjet paper. To align both side, I tried inkjet transparent but those get deformed at some places during printing and it's impossible to align the vias. A part of them are ok while other are only touching by the side.
Taping the transparent on 200g paper didn't help.
Do someone solve this problem ?

Mike.



      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by DJ Delorie

What I've been doing is including a "target" in my prints (four 25 mil
squares in a square, with a 1 mil gap - that translates to a 1 mil ink
crosshair when I print negatives).  I print this on all photomasks and
one on plain paper.  The plain paper one I use to pre-drill 16 mil
holes at each crosshair.  Then, when exposing, I can line up the holes
with the crosshairs pretty accurately, and double-check through the
glass overlay.

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Michel Baguet

Well, line up is not a problem. it's the transparent getting deformed when heated.

--- On Fri, 7/4/08, DJ Delorie <dj@...> wrote:
Show quoted textHide quoted text
From: DJ Delorie <dj@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 5:50 AM










    
            

What I've been doing is including a "target" in my prints (four 25 mil

squares in a square, with a 1 mil gap - that translates to a 1 mil ink

crosshair when I print negatives).  I print this on all photomasks and

one on plain paper.  The plain paper one I use to pre-drill 16 mil

holes at each crosshair.  Then, when exposing, I can line up the holes

with the crosshairs pretty accurately, and double-check through the

glass overlay.


      

    
    
	
	 
	
	








	


	
	


      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by fana cute

I never try this, but I read from some article (i've forgotten where) that problem is from your ink printer...and the article advised to use epson ink..

--- On Thu, 7/3/08, Michel Baguet <bagmik@...> wrote:
Show quoted textHide quoted text
From: Michel Baguet <bagmik@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Thursday, July 3, 2008, 11:04 PM










    
            Well, line up is not a problem. it's the transparent getting deformed when heated.



--- On Fri, 7/4/08, DJ Delorie <dj@...> wrote:

From: DJ Delorie <dj@...>

Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy

To: Homebrew_PCBs@ yahoogroups. com

Date: Friday, July 4, 2008, 5:50 AM



What I've been doing is including a "target" in my prints (four 25 mil



squares in a square, with a 1 mil gap - that translates to a 1 mil ink



crosshair when I print negatives).  I print this on all photomasks and



one on plain paper.  The plain paper one I use to pre-drill 16 mil



holes at each crosshair.  Then, when exposing, I can line up the holes



with the crosshairs pretty accurately, and double-check through the



glass overlay.



	

	 

	

	



	



	

	



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




      

    
    
	
	 
	
	








	


	
	


      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Dylan Smith

On Thu, 3 Jul 2008, Michel Baguet wrote:

> hi guys,
>
> I got to the point where I can etch 6 mils traces and 32 mils vias with
> a 12 mils hole with inkjet paper.

First, I presume you're using glossy inkjet paper for toner transfer from
a laser printer.

If that's the case you don't need to muck around with transparencies.
Print both sides of the layout to your normal paper, place them together
face in - hold them to a bright light and use the vias to align. Suitable
bright lights are: the sun, a table lamp, or best, a light box where you
can lay it all flat.

Then tape the ends of the paper together at one end, to form a hinge.
Re-check that it's still aligned. If it is, slip the copper board between
the paper and get ironing.

I've done lots of double sided boards this way - never had a failure.

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Harvey White

On Fri, 4 Jul 2008 09:47:55 +0100 (BST), you wrote:

I've always had a conceptual problem doing it exactly this way.  I can
see that if the joint between the two pieces of paper is exactly in
the middle of the board thickness, every thing aligns.  If it's not,
then one layer is offset with respect to the other.

Has anyone considered aligning the masks with a filler made from a
scrap piece of etched board, same thickness, and then perhaps a piece
of plastic to duplicate the board?

Harvey
Show quoted textHide quoted text
>On Thu, 3 Jul 2008, Michel Baguet wrote:
>
>> hi guys,
>>
>> I got to the point where I can etch 6 mils traces and 32 mils vias with
>> a 12 mils hole with inkjet paper.
>
>First, I presume you're using glossy inkjet paper for toner transfer from
>a laser printer.
>
>If that's the case you don't need to muck around with transparencies.
>Print both sides of the layout to your normal paper, place them together
>face in - hold them to a bright light and use the vias to align. Suitable
>bright lights are: the sun, a table lamp, or best, a light box where you
>can lay it all flat.
>
>Then tape the ends of the paper together at one end, to form a hinge.
>Re-check that it's still aligned. If it is, slip the copper board between
>the paper and get ironing.
>
>I've done lots of double sided boards this way - never had a failure.

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Leon

----- Original Message -----
Show quoted textHide quoted text
From: "Harvey White" <madyn@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Friday, July 04, 2008 2:09 PM
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy


> On Fri, 4 Jul 2008 09:47:55 +0100 (BST), you wrote:
>
> I've always had a conceptual problem doing it exactly this way.  I can
> see that if the joint between the two pieces of paper is exactly in
> the middle of the board thickness, every thing aligns.  If it's not,
> then one layer is offset with respect to the other.
>
> Has anyone considered aligning the masks with a filler made from a
> scrap piece of etched board, same thickness, and then perhaps a piece
> of plastic to duplicate the board?

That has been mentioned on this forum before, it's probably the best way to 
do it. A couple of pegs could be used with holes in the transparencies, to 
make the alignment even better. I think that something similar is used by 
the PCB manufacturers - they use dowels with their phototools.

Leon
--
Leon Heller
Amateur radio call-sign G1HSM
Yaesu FT-817ND and FT-857D transceivers
Suzuki SV1000S motorcycle
leon355@...
http://www.geocities.com/leon_heller

RE: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Bertho Boman

Sticking the "tail" or joint between two half thickness spacers (strips)
forces the tail to be in the middle and the artwork aligns.

 

To use the alignment pins suggested a dedicated puncher with fixed spacing
should be used and a way to accurately align the artworks to be punched.  Of
course the fixture pins must also accurately match the punch setup.

Bertho
Show quoted textHide quoted text
From:  Harvey White   Sent: Friday, July 04, 2008 09:09:

I've always had a conceptual problem doing it exactly this way. I can
see that if the joint between the two pieces of paper is exactly in
the middle of the board thickness, every thing aligns. If it's not,
then one layer is offset with respect to the other.

Has anyone considered aligning the masks with a filler made from a
scrap piece of etched board, same thickness, and then perhaps a piece
of plastic to duplicate the board?

Harvey



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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Dylan Smith

On Fri, 4 Jul 2008, Harvey White wrote:

> On Fri, 4 Jul 2008 09:47:55 +0100 (BST), you wrote:
>
> I've always had a conceptual problem doing it exactly this way.  I can
> see that if the joint between the two pieces of paper is exactly in
> the middle of the board thickness, every thing aligns.  If it's not,
> then one layer is offset with respect to the other.

I've never found it to be a problem. I only had bad registration on one
board I've made this way, and even then it wasn't bad enough that the
board couldn't be used. Most of the time the registration is pretty much
spot on. If you need really fine tolerances for small vias then I suspect
a piece of old board in the tape 'hinge' as you suggest would reduce the
risk of mis-registration. I use 0.8mm drill bits, so my vias tend to be
sized for that (except for things like jumper headers where I use 1.0mm
bits), with 10 mil annular rings minimum (so that'd make my largest vias
35 mils, and the smaller ones 30 mils.

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by DJ Delorie

Michel Baguet <bagmik@...> writes:
> Well, line up is not a problem. it's the transparent getting
> deformed when heated.

Ah, that.  What I did was calibrate the deformity once (transfer a 3x3
square to a board and measure it) and compensate for it in PCB.  To
align two sides, I ended up using targets centered on the sides of the
board, rather than diagonally opposite.  Also, I've tried using a hand
iron to tack down the paper before laminating it.

Photomask is easier because there's no heat, you can see through the
paper to line it up, and nothing moves during the exposure.

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by DJ Delorie

Harvey White <madyn@...> writes:
> Has anyone considered aligning the masks with a filler made from a
> scrap piece of etched board, same thickness, and then perhaps a
> piece of plastic to duplicate the board?

Another thing to try is to tape *three* corners, not two.  The extra
tension helps hold the seam centered on the thickness of the board.
Not that I've ever done that; my TT paper is too opaque to line up
that way.  I've pre-drilled target holes in the PCB and poked matching
holes in the TT paper to tack it down in the right place, with some
success.

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Michel Baguet

Using a filler is partway what I'm doing. I put a target at each corner of the two sheets, align them with needles then lift one of the sheet to insert a piece of PCB to get the right space between them. I place the filler outside the printed area but as close as possible from the needles. I tape the two sheet to the filler, remove the needles (the tape is supossed to keep the sheets aligned) and  put the PCB to etch between the sheets, tape the sheet to the PCB and remove the filler.This is many manipulations and whatever you do, alignement is like playing with dices . Some times you win, some times you loose... Especially with 32 mils vias.
This is the reason why I wanted to use transparent for inkjet. But there are two problems, the first is that the transparent get deformed, bended with the heat of the fusing unit inside the laser printer and the second, toner density is very light, even with density set at max. (laserjet 6P) And I'm afraid that the pcb will be etched with a lot of pinhole.
So I believe I'll get back to blind alignement with plain paper by first driling 12 or 16 mils holes at the corner of the pcb to etch and holes in the sheets and align them with needles in the PCB.



--- On Fri, 7/4/08, Harvey White <madyn@...> wrote:
Show quoted textHide quoted text
From: Harvey White <madyn@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 1:09 PM










    
            On Fri, 4 Jul 2008 09:47:55 +0100 (BST), you wrote:



I've always had a conceptual problem doing it exactly this way.  I can

see that if the joint between the two pieces of paper is exactly in

the middle of the board thickness, every thing aligns.  If it's not,

then one layer is offset with respect to the other.



Has anyone considered aligning the masks with a filler made from a

scrap piece of etched board, same thickness, and then perhaps a piece

of plastic to duplicate the board?



Harvey



>On Thu, 3 Jul 2008, Michel Baguet wrote:

>

>> hi guys,

>>

>> I got to the point where I can etch 6 mils traces and 32 mils vias with

>> a 12 mils hole with inkjet paper.

>

>First, I presume you're using glossy inkjet paper for toner transfer from

>a laser printer.

>

>If that's the case you don't need to muck around with transparencies.

>Print both sides of the layout to your normal paper, place them together

>face in - hold them to a bright light and use the vias to align. Suitable

>bright lights are: the sun, a table lamp, or best, a light box where you

>can lay it all flat.

>

>Then tape the ends of the paper together at one end, to form a hinge.

>Re-check that it's still aligned. If it is, slip the copper board between

>the paper and get ironing.

>

>I've done lots of double sided boards this way - never had a failure.


      

    
    
	
	 
	
	








	


	
	


      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Michel Baguet

the main problem is that the transparent get deformed while passing thru the fusing unit of the printer.

--- On Fri, 7/4/08, Leon <leon355@btinternet.com> wrote:
Show quoted textHide quoted text
From: Leon <leon355@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 1:21 PM










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

From: "Harvey White" <madyn@embarqmail. com>

To: <Homebrew_PCBs@ yahoogroups. com>

Sent: Friday, July 04, 2008 2:09 PM

Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy



> On Fri, 4 Jul 2008 09:47:55 +0100 (BST), you wrote:

>

> I've always had a conceptual problem doing it exactly this way.  I can

> see that if the joint between the two pieces of paper is exactly in

> the middle of the board thickness, every thing aligns.  If it's not,

> then one layer is offset with respect to the other.

>

> Has anyone considered aligning the masks with a filler made from a

> scrap piece of etched board, same thickness, and then perhaps a piece

> of plastic to duplicate the board?



That has been mentioned on this forum before, it's probably the best way to 

do it. A couple of pegs could be used with holes in the transparencies, to 

make the alignment even better. I think that something similar is used by 

the PCB manufacturers - they use dowels with their phototools.



Leon

--

Leon Heller

Amateur radio call-sign G1HSM

Yaesu FT-817ND and FT-857D transceivers

Suzuki SV1000S motorcycle

leon355@btinternet. com

http://www.geocitie s.com/leon_ heller 




      

    
    
	
	 
	
	








	


	
	


      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Michel Baguet

Do you use plain paper ?

--- On Fri, 7/4/08, Dylan Smith <dyls@...> wrote:
Show quoted textHide quoted text
From: Dylan Smith <dyls@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 3:38 PM










    
            On Fri, 4 Jul 2008, Harvey White wrote:



> On Fri, 4 Jul 2008 09:47:55 +0100 (BST), you wrote:

>

> I've always had a conceptual problem doing it exactly this way.  I can

> see that if the joint between the two pieces of paper is exactly in

> the middle of the board thickness, every thing aligns.  If it's not,

> then one layer is offset with respect to the other.



I've never found it to be a problem. I only had bad registration on one

board I've made this way, and even then it wasn't bad enough that the

board couldn't be used. Most of the time the registration is pretty much

spot on. If you need really fine tolerances for small vias then I suspect

a piece of old board in the tape 'hinge' as you suggest would reduce the

risk of mis-registration. I use 0.8mm drill bits, so my vias tend to be

sized for that (except for things like jumper headers where I use 1.0mm

bits), with 10 mil annular rings minimum (so that'd make my largest vias

35 mils, and the smaller ones 30 mils.


      

    
    
	
	 
	
	








	


	
	


      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Michel Baguet

The transparent is already deformed when passing thru the fusing unit of the printer and the
the deformation are not regular. For exemple, the corners align well while the top center is too low, the center is on the left and the center bottom is on the right... and so on.
Different print give different deformation positions.

--- On Fri, 7/4/08, DJ Delorie <dj@...> wrote:
Show quoted textHide quoted text
From: DJ Delorie <dj@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 4:07 PM










    
            

Michel Baguet <bagmik@yahoo. com> writes:

> Well, line up is not a problem. it's the transparent getting

> deformed when heated.



Ah, that.  What I did was calibrate the deformity once (transfer a 3x3

square to a board and measure it) and compensate for it in PCB.  To

align two sides, I ended up using targets centered on the sides of the

board, rather than diagonally opposite.  Also, I've tried using a hand

iron to tack down the paper before laminating it.



Photomask is easier because there's no heat, you can see through the

paper to line it up, and nothing moves during the exposure.


      

    
    
	
	 
	
	








	


	
	


      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Michel Baguet

What do you mean by "some succes" ? Is-it often, 3 out of 5, or less ?
Is there a big off-registration ?

--- On Fri, 7/4/08, DJ Delorie <dj@delorie.com> wrote:
Show quoted textHide quoted text
From: DJ Delorie <dj@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 4:09 PM










    
            

Harvey White <madyn@embarqmail. com> writes:

> Has anyone considered aligning the masks with a filler made from a

> scrap piece of etched board, same thickness, and then perhaps a

> piece of plastic to duplicate the board?



Another thing to try is to tape *three* corners, not two.  The extra

tension helps hold the seam centered on the thickness of the board.

Not that I've ever done that; my TT paper is too opaque to line up

that way.  I've pre-drilled target holes in the PCB and poked matching

holes in the TT paper to tack it down in the right place, with some

success.


      

    
    
	
	 
	
	








	


	
	


      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Leon

----- Original Message -----
Show quoted textHide quoted text
From: "Michel Baguet" <bagmik@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Friday, July 04, 2008 5:40 PM
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy


> the main problem is that the transparent get deformed while passing thru 
> the fusing unit of the printer.

I think it only works properly when printing transparencies on an inkjet 
printer.

Leon
--
Leon Heller
Amateur radio call-sign G1HSM
Yaesu FT-817ND and FT-857D transceivers
Suzuki SV1000S motorcycle
leon355@...
http://www.geocities.com/leon_heller

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by DJ Delorie

Try using laser transparencies instead of inkjet transparencies
(assuming the toner will release afterwards).

The pin trick is easier if you pre-poke the holes from the toner side,
so you can tell where they are.

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by DJ Delorie

Michel Baguet <bagmik@...> writes:
> What do you mean by "some succes" ? Is-it often, 3 out of 5, or
> less?  Is there a big off-registration ?

Keep in mind I use 6/6 rules with 13 mil via drills, so "some success"
for me might be "just fine" for you.  Success for me is within 4-5
mils of dead center; I use my 13 mil drills as the pins.  It's a lot
of hassle, but if you take your time it does come out correct.

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Michel Baguet

indeed for uv exposure but I'm doing toner tranfer

--- On Fri, 7/4/08, Leon <leon355@...> wrote:
Show quoted textHide quoted text
From: Leon <leon355@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 5:13 PM










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

From: "Michel Baguet" <bagmik@yahoo. com>

To: <Homebrew_PCBs@ yahoogroups. com>

Sent: Friday, July 04, 2008 5:40 PM

Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy



> the main problem is that the transparent get deformed while passing thru 

> the fusing unit of the printer.



I think it only works properly when printing transparencies on an inkjet 

printer.



Leon

--

Leon Heller

Amateur radio call-sign G1HSM

Yaesu FT-817ND and FT-857D transceivers

Suzuki SV1000S motorcycle

leon355@btinternet. com

http://www.geocitie s.com/leon_ heller 




      

    
    
	
	 
	
	








	


	
	


      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Michel Baguet

A few days ago, I read on HP website that they are using a special mean to fuse the toner with the transparent so no possible release .

--- On Fri, 7/4/08, DJ Delorie <dj@...> wrote:
Show quoted textHide quoted text
From: DJ Delorie <dj@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 5:49 PM










    
            

Try using laser transparencies instead of inkjet transparencies

(assuming the toner will release afterwards).



The pin trick is easier if you pre-poke the holes from the toner side,

so you can tell where they are.


      

    
    
	
	 
	
	








	


	
	


      

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

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Michel Baguet

Good idea, using the drill bits as a guide to align the sheet, same diameter as the holes should avoid misalignment

--- On Fri, 7/4/08, DJ Delorie <dj@...> wrote:
Show quoted textHide quoted text
From: DJ Delorie <dj@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 5:51 PM










    
            

Michel Baguet <bagmik@yahoo. com> writes:

> What do you mean by "some succes" ? Is-it often, 3 out of 5, or

> less?  Is there a big off-registration ?



Keep in mind I use 6/6 rules with 13 mil via drills, so "some success"

for me might be "just fine" for you.  Success for me is within 4-5

mils of dead center; I use my 13 mil drills as the pins.  It's a lot

of hassle, but if you take your time it does come out correct.


      

    
    
	
	 
	
	








	


	
	


      

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

RE: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-04 by Bertho Boman

Why blind alignment?  Crank up enough backlight and you should be able to
see through the paper.
Bertho

From Michel Baguet     Sent: Friday, July 04, 2008 12:39

----> snip
So I believe I'll get back to blind alignment with plain paper by first
drilling 12 or 16 mils holes at the corner of the pcb to etch and holes in
the sheets and align them with needles in the PCB.

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-06 by Philip Pemberton

Bertho Boman wrote:
> Why blind alignment?  Crank up enough backlight and you should be able to
> see through the paper.

Perhaps a strobe light would be powerful enough. Assuming you could get used 
to the flickering :)

But seriously, what about this --

1 piece of FR4, 1.6mm (assuming that's what you're using to make the PCBs). 
Remove the copper, either by etching or sanding. Cut it into four 2"x0.5" strips.

Drill a tiny - as in roughly the size of the needle - hole in each corner, 
about a quarter inch in from the top and left edges. Do the same thing for all 
four strips.

Push four thin needles into the holes. Ideally these should push in and fit 
tightly. Also put some double-sided tape on the FR4. Both sides :)

Now print your pattern with alignment holes ~2x0.5" away from the corners. 
Take one sheet of paper and push it onto the needles. Check alignment and 
remove the tape from each piece of FR4 in turn. Stick them down. Now put your 
PCB in the middle and do the same for the other side, align as before, stick 
down and remove the needles.

Iron the board and cross your fingers...

I'm still working on finding a decent TT paper that's still in production. 
Seems HP Everyday doesn't work any more... Still, it works in the inkjet (a 
rebuilt Epson C86 loaded with dye based ink) so it's not a total waste...

-- 
Phil.
ygroups@...
http://www.philpem.me.uk/

Re: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-06 by Michel Baguet

I just find a way to solve the print geometry problem. Now I'm going to test blind alignment with needles and holes in the PCB of the same diameter.

--- On Sun, 7/6/08, Philip Pemberton <ygroups@...> wrote:
Show quoted textHide quoted text
From: Philip Pemberton <ygroups@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Sunday, July 6, 2008, 7:45 AM










    
            Bertho Boman wrote:

> Why blind alignment?  Crank up enough backlight and you should be able to

> see through the paper.



Perhaps a strobe light would be powerful enough. Assuming you could get used 

to the flickering :)



But seriously, what about this --



1 piece of FR4, 1.6mm (assuming that's what you're using to make the PCBs). 

Remove the copper, either by etching or sanding. Cut it into four 2"x0.5" strips.



Drill a tiny - as in roughly the size of the needle - hole in each corner, 

about a quarter inch in from the top and left edges. Do the same thing for all 

four strips.



Push four thin needles into the holes. Ideally these should push in and fit 

tightly. Also put some double-sided tape on the FR4. Both sides :)



Now print your pattern with alignment holes ~2x0.5" away from the corners. 

Take one sheet of paper and push it onto the needles. Check alignment and 

remove the tape from each piece of FR4 in turn. Stick them down. Now put your 

PCB in the middle and do the same for the other side, align as before, stick 

down and remove the needles.



Iron the board and cross your fingers...



I'm still working on finding a decent TT paper that's still in production. 

Seems HP Everyday doesn't work any more... Still, it works in the inkjet (a 

rebuilt Epson C86 loaded with dye based ink) so it's not a total waste...



-- 

Phil.

ygroups@philpem. me.uk

http://www.philpem. me.uk/


      

    
    
	
	 
	
	








	


	
	


      

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RE: [Homebrew_PCBs] double sided PCB, accuracy

2008-07-06 by Bertho Boman

Try a regular good flash light or a halogen desk lamp.  It works
surprisingly well.

A related trick if this method is used is to not use two identical targets
as is normally done.  Instead use complimentary targets.  For example, on
one layer use concentric circles of 5 mil lines and 5 mil spacing.  On the
other layer use the same dimensions but start with a space and then a black
line.  In other words, you will have a positive and a negative target.
  When placed on top of each other and viewed with light from below they
will turn all black only when perfectly aligned.  Any error is very obvious.

Another comment:
Taping just a hinge allows a slight movement of the layers since the hinge
allows a microscopic movement.  Cut off the corners of the top layer where
the hinge will normally be placed. Placing tape on those corners really
locks the artwork together without any movement.

Finally, place two half thickness spacers one on each side of the tail to
force it to be in the center when the board is put under the glass for
exposure. For ironing use just one half sized spacer on the bottom and push
the tail down on it to keep the top and bottom aligned.
Bertho
=================================
Show quoted textHide quoted text
From: Philip Pemberton  Sent: Sunday, July 06, 2008 03:45

Bertho Boman wrote:
> Why blind alignment? Crank up enough backlight and you should be able to
> see through the paper.

Perhaps a strobe light would be powerful enough. Assuming you could get used

to the flickering :)

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