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'[PIC]: Double side PCB - Again...'
2002\05\13@045153 by Tal Bejerano - AMC

flavicon
face
Hi 2 All

It seems hopeless for me to do one side pcb, eagle didn't have success in
one side auto route.
so I have to move to two sided pcb.
I've seen some discussions about double side methods but I am looking for
the best way, folding transparency sheet look to me not to accurate, can
anyone suggest other better ways?
I am desperate!

Regards

Tal Bejerano
AMC - ISRAEL

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2002\05\13@050459 by Alan B. Pearce

face picon face
>It seems hopeless for me to do one side pcb, eagle didn't have
>success in one side auto route.
>so I have to move to two sided pcb.

You could try looking at the layout with your eyeballs, and see if you can
manually re-arrange the tracks to get it all in, possibly with a small
number of wire jumpers if you really want to use single sided PCB..

However you may find there is no price advantage having a single sided PCB
over a double sided PCB, because the board house may not carry stocks of
single sided board, and so would have to etch away all the copper on the
second side. Check with your PCB house if the cost is a major factor.

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2002\05\13@051749 by Tal Bejerano - AMC

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well I am doing my own pcb @ home.
no need for board house.


Regards

Tal Bejerano
AMC - ISRAEL


-----Original Message-----
From: pic microcontroller discussion list
[spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU]On Behalf Of Alan B. Pearce
Sent: Monday, May 13, 2002 11:04 AM
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: Re: [PIC]: Double side PCB - Again...


>It seems hopeless for me to do one side pcb, eagle didn't have
>success in one side auto route.
>so I have to move to two sided pcb.

You could try looking at the layout with your eyeballs, and see if you can
manually re-arrange the tracks to get it all in, possibly with a small
number of wire jumpers if you really want to use single sided PCB..

However you may find there is no price advantage having a single sided PCB
over a double sided PCB, because the board house may not carry stocks of
single sided board, and so would have to etch away all the copper on the
second side. Check with your PCB house if the cost is a major factor.

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2002\05\13@060401 by Alan B. Pearce

face picon face
>well I am doing my own pcb @ home.
>no need for board house.

OK fair enough. I guess then it comes down to eyeballing the layout as far
as the autorouter has got to see where you can improve it.

FWIW many people will use the autorouter only as a starting point in the
layout, and then go through eliminating vias and unnecessary tracking as
appropriate afterwards.

Unless your board is very simple, rather large, or has lots of layers, there
is a very good chance the autorouter will not do it all for you.

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2002\05\13@062317 by Andrei B.

picon face
--- Tal Bejerano - AMC <kooterspamKILLspamZAHAV.NET.IL> wrote:
> Hi 2 All
>
> It seems hopeless for me to do one side pcb, eagle didn't have
> success in
> one side auto route.
> so I have to move to two sided pcb.
> I've seen some discussions about double side methods but I am looking
> for
> the best way, folding transparency sheet look to me not to accurate,
> can
> anyone suggest other better ways?


Two suggstions :
1) in some other PCB design software I could force them to do one-sided
routing by defining both layers used as _bottom_

2) print the drill mask too and drill 4 holes near each corner. If you
have holes for mounting screws, all the better.

If you are using prefab plates with resist on them :

Use these holes to guide the placement of your transparency sheet.
Put it on one side only. Expose, having the other side protected from
UV light.
Repeat with the other side. Use the holes to align correctly your
sheet.

Have enough solution so that you can immerse the plate vertically and
you can watch both sides with ease for progress.

Wash then go to etching, plate also vertically.

If you are using spray:
spray one side, expose, develop, wash.
spray the other side, then etch first side.
Expose side2, and expose side1 uncovered so the protective resist will
be developed as exposed when developing side2.
wash.
use a protective spray on side1 (I use FLUX SK10 which adds a layer of
protective coating which also helps the soldering process).
etch, wash, clean up the remaing resist, add protective coat.




=====
ing. Andrei Boros
Centrul pt. Tehnologia Informatiei
Societatea Romana de Radiodifuziune

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2002\05\13@101253 by Olin Lathrop

face picon face
> It seems hopeless for me to do one side pcb, eagle didn't have success in
> one side auto route.
> so I have to move to two sided pcb.
> I've seen some discussions about double side methods but I am looking for
> the best way, folding transparency sheet look to me not to accurate, can
> anyone suggest other better ways?
> I am desperate!

Use a board house.  Unless you time is worth absolutely nothing, you can't
compete with having it done professionally.


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(978) 742-9014, http://www.embedinc.com

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2002\05\13@115959 by Spehro Pefhany

picon face
At 10:04 AM 5/13/02 +0100, you wrote:


>However you may find there is no price advantage having a single sided PCB
>over a double sided PCB, because the board house may not carry stocks of
>single sided board, and so would have to etch away all the copper on the
>second side. Check with your PCB house if the cost is a major factor.

In general 2-sided boards made in developed countries in small to moderate
quantities (up to 10,000 maybe) are about the same price as 1-sided. If you
go with punched 1-sided boards and paper-based phenolic, the price can be
VERY much cheaper per square inch, especially from offshore. But you have
to buy the punch dies and order a fair number at once.

Even relatively good programs have poor auto-routing for single-sided
patterns (note that SMT on both sides leads to single-sided-like routing,
so things are improving). I find a pad of squared paper and a pencil
works well for small single-sided boards. Placement is VERY important
in single-sided board design.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2002\05\13@123158 by Pic Dude

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face
I thought so to, but never had a problem with this -- I did start off by
putting
small "targets" (crosshairs) on the pattern, drilling small holes before
etching
and lining up the targets with these holes on both sides.

However, I found that folding and actually making an envelope (credit to
someone else on this list whose name escapes me, sorry) with 3 sides
stapled together, works well.  It helps to leave a lot of extra transparency
overhanging off the PCB.

Cheers,
-Neil.


{Original Message removed}

2002\05\13@131135 by Tal Bejerano - AMC

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face
Olin and others

10x for helping.
about board house, in my country the minimum price I got for prototype pcb
was 300-500 US$! I'm talking about one or two pcbs. maybe the price will go
low everyday lets say to 100US$ still to much for me right now.
and don't forget that if I do at home all of the process will cost me LESS
then 6$!!!!.
this is the reason why to do it at home. I can make many prototypes very
cheap just need to find info how to do it the best way.

Ex:
1 sheet transparency - 0.25 $
etch material - 1 $
develop material 0.10 $
1 10x16cm one side board - 5$
1 10x16cm two side board - 5.5$
60cm UV light (that I can use many times) 20$

Regards

Tal Bejerano
AMC - ISRAEL


{Original Message removed}

2002\05\14@144720 by Peter L. Peres

picon face
On Mon, 13 May 2002, Tal Bejerano - AMC wrote:

>Hi 2 All
>
>It seems hopeless for me to do one side pcb, eagle didn't have success in
>one side auto route.
>so I have to move to two sided pcb.
>I've seen some discussions about double side methods but I am looking for
>the best way, folding transparency sheet look to me not to accurate, can
>anyone suggest other better ways?
>I am desperate!

What 'folding transparency sheet' looks to you depends mostly on your eyes
and other receptors. It is as accurate as you dare to make it, especially
if you put fiducials on both sides so they align.

Peter

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2002\05\14@155907 by Dwayne Reid

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On Mon, 13 May 2002, Tal Bejerano - AMC wrote:
>folding transparency sheet look to me not to accurate, can
>anyone suggest other better ways?

Take a scrap of copper clad PCB material and make an L shaped piece with 3"
X 4" long legs about 3/4" wide.  In other words, shaped like a carpenter's
square.

Tape one transparency to both arms.  Flip the whole thing over and very
carefully line up the other transparency.  Tape one edge only - to the
longer arm.  The tape is your hinge.

I like to leave about 1/4" of border around all sides of the PCB.  Be sure
to place the transparencies such that you leave at least some border -
don't try to position the edges of the finished board right at the edge of
the L shaped holder.

Tuck your sensitized board into the pocket formed by the transparencies and
holder.  Put it into the exposure frame and expose.

The reason for taping one transparency to only the long arm is to allow for
easy removal of the exposed PCB.  After exposure, the photo-sensitive
laminate sticks to the transparencies.  But since the one transparency is
taped on 1 edge only, you can peel it away from the PCB without damaging
either and without changing the registration.

I've been making double sided boards this way since the mid 70's.  It works
and its easy!

dwayne


Dwayne Reid   <EraseMEdwaynerspam_OUTspamTakeThisOuTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 18 years of Engineering Innovation (1984 - 2002)
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2002\05\14@162111 by Andy Shaw

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Hi Dwayne,
Since I'm going to be going down this road soon I'd like to understand how
to make this work...

{Original Message removed}

2002\05\14@180103 by Peter L. Peres

picon face
On Tue, 14 May 2002, Andy Shaw wrote:

>Hi Dwayne,
>Since I'm going to be going down this road soon I'd like to understand how
>to make this work...

The L shaped scrap board acts as a spacer between the films so they align
perfectly (w/o the scrap they are inclined between the taped edges and the
useful film - this causes some misalignment - as someone else said, it is
smaller if the taped parts are farther away from the active part).

Peter

>
>{Original Message removed}

2002\05\14@183154 by Pic Dude

flavicon
face
Peter's got the right solution here.

I've done this too in the recent past, and the process
actually works well, except that I've found it a little
tricky to keep the board tucked into the corner of the
'L' when laying the plexiglass on top (the piece that
came with the UV light).  The transparency is just too
slippery and flexible.  So I got 2 small pieces of glass,
and clamped it to either side of the setup, and could
then have less sliding around when the PCB is in the
"pocket".

The "layers" in this contraption are now: glass,
transparency, L-shaped PCB, transparency, and glass.

So as not to have to remove the PCB again, I peel off
the white protective cover on both sides and slip the
PCB in the "pocket", but then slip a piece of black
card between the transparency and glass on one side
to cover it while exposing the other side.  With the
rigid glass in place, the unit can be exposed sitting
vertically (on an edge).  You actually need to sit
it upright or on some other thing cause the clamps
get in the way of it sitting on a flat table.

To line up the transparencies before taping to the
"L", I put targets/cross-hairs in the corners of
the PCB layout, put the 2 sheets together, and
punched thru the crosshairs with pins.  When the
"L" was slipped in between, the orientation of the
pins prevented any parallax mis-alignment.

Only other thing I thought of doing, but never got
around to, was to come up with some arrangement of
mirrors to be able to expose both sides simultaeously.

A little work, a few other materials, and bit more
time, and excellent results.  However, I got the
transparency pocket to work well (by stapling 3 sides
instead of just folding), so I don't really bother
with the whole glass/"L" thing.

And to contradict all of this, I just use a PCB
house now. :-)

Cheers,
-Neil.




{Original Message removed}

2002\05\14@201411 by Dwayne Reid

flavicon
face
At 09:19 PM 5/14/02 +0100, Andy Shaw wrote:

>Ok what is the "exposure frame" and how do you do the exposure. My UV box
>will only allow a single side to exposed at a time. So how do I ensure
>things don't move between exposing one side and the other. Is this what the
>frame is for? What does it look like?

The exposure frame is 2 pieces of glass.  Mine are about 12" square but you
just need to make them larger than the largest board you intend to expose.

You need a way to clamp together the sandwich formed by the glass frame and
the transparencies / PCBs.  I use vacuum - there is a soft foam
weatherstripping surrounding the perimeter of one of the pieces of glass
and a hole bored the glass (inside the perimeter).  I use an old Gast
vacuum pump that delivers about 15" Hg.  But clamps of any sort will work
almost as well as vacuum.  I'd think that those big black spring-steel
paper clips would work just fine.

The reason for 2 pieces of glass is so that the clamping pressure does not
get removed until both sides of the PCB have been exposed.  I also have
rubber feet at the corners on both sides of the exposure frame.  That helps
ensure that the glass does pick up debris while that face is down.

You will have to determine your exposure time for your setup.  I use a 175W
Mercury Vapor bulb (from a standard yard light) with the outer glass
envelope removed.  There are 2 basic types of bulb out there: those with a
frosted outer envelope and those with a clear outer envelope.  I found that
the frosted bulbs (with that frosted envelope removed) worked best for my
setup.

My exposure lamp has a motorized shutter on it, controlled by the
timer.  No one is allowed to remain in the room while the shutter is open.

After all the board has been prepped and laminated with the Riston
photo-sensitive laminate, I turn on the expose lamp and wait for it to warm
up fully (about 10 minutes).  All I do then is stick the neg and PCB into
the frame, hit the vacuum switch, center the frame under the lamp, hit the
shutter timer start button, then leave the room and wait for the beeper
that signals the end of the expose time.  If its a double sided board, flip
the frame over (vacuum stays on) and expose the other side.

I don't bother covering the opposite side of the expose frame when I'm
exposing a double sided board.  It doesn't seem to matter!  I assume that
is because the plywood surface that the frame is sitting on is fairly dark
and does not reflect much light onto the under-side of the expose frame.

My expose distance is 12" and the timer is set for 130 seconds.  As I
mentioned, that's what works for MY setup.  Yours will be different.

The best way to determine the optimum exposure time is by using an exposure
calculator.  I have a couple of them - one is from Autotype, the other is
marked Stouffer.  Each of these is a piece of film with a repeated pattern
on it and a different grade of neutral density filter over each
pattern.  The Stouffer unit has the most steps (21) - its what I used to
determine the best exposure time.  You expose the board with double the
expected time, develop and etch, then see which target has the best
resolution.  If your expected exposure time is correct, the middle (50%)
target will be the best.  If not, multiply the total exposure time by the
multiplier at the best target and re-try (using that time as the expected
exposure time).  The one from Autotype is the also useful: it has only 5
steps but the targets allow you to determine final resolution.  According
to the Autotype unit, I get about 0.002" resolution (the limit of the
target) when everything goes perfectly.

dwayne


Dwayne Reid   <dwaynerspamspam_OUTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 18 years of Engineering Innovation (1984 - 2002)
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2002\05\14@203656 by Peter L. Peres

picon face
On Tue, 14 May 2002, Pic Dude wrote:

>Peter's got the right solution here.

Actually Dwayne Ried (?) had the L posting, I just explained it.

I seldom use the L, I use taped foils and double glass exposure frame. The
alignment is aided by putting fiducials OUTSIDE the board and by tacking
one of the foils to a corner of the board with a tiny bit of blu-tack or
hot glue (only one side). Once I close the glass frame, I do not open it
anymore until both sides are exposed. I expose one side then the other. No
black carton is used on the 'other' side, but the exposure table is black.
Side light to the lower layer never was a problem for me. The fiducials
outside the board allow perfect alignment without fudging with the board.
I often make small prototypes that have real funny shapes so I make them
from copper clad and spray photoresist on them after I cut them to shape.
This is a pain but the board house would bankrupt me for the 3-4 tries I
need to get everything right (see Tal's posting for prices around here).
Resist board cannot be cut without chipping the resist, even though I use
a jeweller's saw with 000 blades that cost a fortune each.

Peter

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2002\05\15@123908 by Peter L. Peres

picon face
On Tue, 14 May 2002, Dwayne Reid wrote:

>After all the board has been prepped and laminated with the Riston
>photo-sensitive laminate, I turn on the expose lamp and wait for it to warm
>up fully (about 10 minutes).  All I do then is stick the neg and PCB into
>the frame, hit the vacuum switch, center the frame under the lamp, hit the
>shutter timer start button, then leave the room and wait for the beeper
>that signals the end of the expose time.  If its a double sided board, flip
>the frame over (vacuum stays on) and expose the other side.

What happens to the vacuum hose that goes through the glass when you flip
it over ? Are the rubber feet tall ?

>My expose distance is 12" and the timer is set for 130 seconds.  As I
>mentioned, that's what works for MY setup.  Yours will be different.

;-) I use spray-on photoresist from CRC in Belgium (I think) and ready
made no-name resist coated boards. Both like 5 minutes at 40cm with 250W
high pressure mercury lamp. Your laminate seems to be more sensitive.

{Quote hidden}

This is the best method but it is expensive (unless you have them). You
can do this to determine same (requires some exposure to the light -
beware):

Take a strip of board about 2cm wide and 10cm long and two strips of
cardboard slightly wider and longer. Cut a pattern in one of the
cardboards, 5 times (you can make a film that repeats 5 patterns instead,
each within 2x2cm. Tape the film on the board, then cover all but one
pattern with the whole black cardboard, expose 2 minutes, expose the next
pattern by moving the black cardboard away, expose 1 more minute, repeat.
You will have 5 patterns corresponding to 2,3,4,5 and 6 minutes. Develop
the board and you will know what you need to use. Do not expose yourself
to the UV light (get out of the room etc). My lamp is housed in an
ex-paint solvent can (1 gallon size) with a timer from a microvawe oven.

There is one more trick: You can copy and expose designs from magazines or
printed on (thin) usual paper by wetting the paper with light oil or even
water. The creep that goes with it does not seem to be noticeable. The
fluid makes the paper transparent. Increase exposure by 30 seconds if
using this. In some countries they sell a suitable product as a spray
(Klarpausspray in German). It evaporates after a few hours unlike the oil.
DO NOT use alcohool of any kind or other solvents for paper wetting for
exposure. They can catch fire under UV.

Peter

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2002\05\16@082742 by Olin Lathrop

face picon face
>It seems hopeless for me to do one side pcb, eagle didn't have success in
>one side auto route.
>so I have to move to two sided pcb.
>I've seen some discussions about double side methods but I am looking for
>the best way, folding transparency sheet look to me not to accurate, can
>anyone suggest other better ways?
>I am desperate!

If you want to make a single sided PC board yourself, try telling Eagle it
is a double sided board but make the cost for routing in the top layer very
high and use lots of optimization passes.  If the number of top layer traces
is then pretty small, you could implement them as hand soldered jumpers.


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(978) 742-9014, http://www.embedinc.com

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2002\05\16@165657 by Andy Shaw

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----- Original Message -----
From: "Olin Lathrop" <RemoveMEolin_piclistTakeThisOuTspamEMBEDINC.COM>
> If you want to make a single sided PC board yourself, try telling Eagle it
> is a double sided board but make the cost for routing in the top layer
very
> high and use lots of optimization passes.  If the number of top layer
traces
> is then pretty small, you could implement them as hand soldered jumpers.

on a related topic anyone know a good way to set up a specctra (7.1 I think)
autorouter to do a similar thing. This thing has more config options than
you would believe and I use it just often enough to ensure I've forgotten
everything by the next time I use it..... But it does seem to do a good job
of auto routing and I like the way it spreads tracks and mitres them....

Andy

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