Hi David and list

I am quite interested in this post too.

I have wanted to fabricate my own PCBs for several years now but I have
never made an attempt. I am set up here to do silk screening and I have
ovens and a hot-air soldering iron. Has anyone else tried to fabricate
their own boards or is the price of farming the work out just so low now?

If anyone has farmed out work, could you please feedback as to the entry
level costs and if possible, some suggested companies?

P.S Many of the boards I want to fabricate are replacements for obsolete
ones. Is there a way to split the layers of an old board apart to study
them?

Thanks-Patrick

David C. Partridge wrote:

Dave,

I do that sort of work for a living and a hobby. I'd be happy to
generate PC board artwork for you in exchange for one unit of the
finished product.

Perhaps you could post a schematic diagram, and I could evaluate it further.

Answers to your specific questions below.

At 7:19 PM +0100 6/2/08, David C. Partridge wrote:

I'd recommend SMT because the parts have much lower parasitics than
thru-hole parts, and they're much more widely available.

It is not at all difficult to solder SOIC, QFPs, chip resistors and
capacitors, etc. to a PC board with a microscope, a soldering iron
and the right type of solder and liquid flux. I do it all the time,
even at home, QFPs down to 0.5mm pitch and components down to 0603
size.

Two layers is reasonable for most analog-type circuits, since with
proper component placement there are hardly any vias. A ground plane
is used on the bottom of the board.

If you have need for high density (small PC board size requirements),
then a four-layer board is a good idea, otherwise a 2-layer will work
in many cases. It really depends on the circuit requirements.

There is absolutely no reason to have a separate layer for digital
ground versus analog ground. One ground plane is plenty. Just
segregate the noisy stuff from the sensitive stuff by putting them in
different parts of the board.

--

--David Forbes, Tucson, AZ
http://www.cathodecorner.com/

David and Patrick,
Check out the following two sites to get an idea of the
current costs to have a custom made board produced.

http://www.pcb123.com/
http://www.expresspcb.com/index.htm

Richard

For one-off PCBs, I've had good luck with www.batchpcb.com .  They work by
panelizing different orders together, so it can sometimes take a month or
more to get your board back.  That's especially true of 4-layer boards,
since it takes longer for them to accumulate enough 4-layer orders to make a
panel.

SMD is not hard to work with by hand, down to 0603 or thereabouts depending
on eyesight and/or equipment.  I find it easier to deal with than
through-hole, frankly.  There are plenty of different ways to solder SMD
ICs, ranging from toaster ovens and heat guns to creating deliberate bridges
which you clean up with solder wick.

-- john, KE5FX

David,

These are the ones we've used. I am sure there are many others.
Prototypes -- www.pcbfabexpress.com
Production -- www.pcbnet.com

An assembly shop can x-ray them for you.

Regards,
Abdul

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Patrick
Sent: Monday, June 02, 2008 11:31 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] PCB design questions thread II

Hi David and list

I am quite interested in this post too.

I have wanted to fabricate my own PCBs for several years now but I have
never made an attempt. I am set up here to do silk screening and I have
ovens and a hot-air soldering iron. Has anyone else tried to fabricate
their own boards or is the price of farming the work out just so low now?

If anyone has farmed out work, could you please feedback as to the entry
level costs and if possible, some suggested companies?

P.S Many of the boards I want to fabricate are replacements for obsolete
ones. Is there a way to split the layers of an old board apart to study
them?

Thanks-Patrick

Hi David:

1. There are many benefits of using Surface Mount Devices (SMD).  In addition
   to the reduction in board area just because the part is smaller there's also a
   major reduction in board area because of the lack of through holes, i.e. you
   get to use both sides of the board (doubling the area).  Classic through hole
   parts are on a 0.1" pitch and most surface mount parts are on some sub multiple
   of that such as 0.05", 0.025", etc.  and either true inches or metric
   equivalent or rounded metric equivalent pitch.  With a fine pointed soldering
   iron I (old guy) can solder 0.05" pitch parts.
   http://www.prc68.com/I/SMT.shtml#Iron
   http://en.wikipedia.org/wiki/Small-Outline_Integrated_Circuit

2. If you use a low cost commercial service like ExpressPCB then you have your
   choice of double sided or four layer.  The four layer has ground and Vcc on the
   inside.

I like their service which now includes schematic and layout applications.
Before when they had just the layout it was purely a mechanical process and
easy to make mistakes (shorted or open traces).  Now, when the schematic is
linked to the layout you can check each node's connections and mistakes are
much less likely.  Both packages are free and in my opinion much easier to
learn than the generic PCB design software packages.  I choose ease of use
rather than to have generic board and drill files.  The latter would make sense
if you were going to make thousands of boards.  I at most make hundreds of boards.

2b)  If working with a double sided board I think you'll find that many ICs
have a recommended layout that requires ground on the top surface.  For example
op amp inputs may need a guard ring around the inputs or a switching circuit
may need ground immediately adjacent to caps.

It's not uncommon to have a board with an analog section and a digital section
and the layout is different in the two sections.  If you look in the archives
there was a comment about how grounds are handled in one of the small boards
that John Ackerman makes I think relating to using a loop for ground or a tree
structure where there are no loops.

I haven't been doing PCBs recently but think the eight inch shear, which has
not worked too well so far, might work for cutting PCBs if the blade is aligned
properly.  http://www.prc68.com/I/8MSB.shtml  With a good way to cut boards you
can put multiple designs on a panel then you cut them apart.  A money saver for
prototypes.

Have Fun,

Brooke Clarke
http://www.prc68.com/P/Prod.html  Products I make and sell
http://www.prc68.com/Alpha.shtml  All my web pages listed based on html name
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Web Cam

David C. Partridge wrote:

On Monday 02 June 2008 02:31:18 pm Patrick wrote:

I've played with doing them at work.  Found it better to just farm them out
to the prototype house.  It is tough to get any real consistency from week to
week.

Cheapest place I've come across for easy boards with 10mil or large lines
is this one, but I've not used them yet (probably next month I will):

http://www.futurlec.com/PCBService.shtml

SMT is actually easier if you have a good magnifying system.  I use
macro-lenses on the wife's Cam-Corder:

http://www.designer-iii.com/Solder/  Looks better than the picture of the
screen shows in reality.

http://www.micromark.com/ has the type of tools that you need, like insulated
and cross-tweezers (squeeze them to open them, the reverse of normal
tweezers) etc.

Pick up a small convection oven at Wal-Mart or such place.

If your making several get a Stencil:

http://www.smtstencil.com/
http://www.customlasercutting.com/

In the long term, yes.  A lot of older TH parts have not been updated to ROHS
(Lead Free) and they never will be, they will be discontinued at some point.
Virtually all new parts are SMT.

I assume that is a typo?  You can not have an odd number of layers.
In this current 3D reality each layer has two sides.  :-)

Separate ground planes, or split ground planes are a bad idea in this context.
Always think about where the return current is going to flow.
Read the Analog Devices seminar notes on the subject.

http://www.analog.com/analog_root/static/library/technicalSeminarSeries.html
is the link to the books but you can find the chapters on line.

Read 7a & 7b if nothing else:

http://www.analog.com/en/DCcList/0,3090,1073%255F%255F961,00.html

--
http://www.wearablesmartsensors.com/
http://www.softwaresafety.net/ http://www.designer-iii.com/
http://www.unusualresearch.com/

Quoth Bob Paddock at 2008-06-03 10:04...

I was looking at these - they actually do overseas shipments for
near-domestic freight prices.  Great for those of us living in countries
where board houses require arm, leg and first-born for even small/simple
jobs.

--
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
LinkedIn: http://www.linkedin.com/in/smiffy

Bob Paddock wrote:

Sure you can.  I have done 3 layer, 5 layer, and 7 layer boards.

Having done those, I will advise you not to do 3 layer, it warps.  But
everything else is easily do able.

Multilayer boards are done by bonding together combinations of
1 side, 2 side, and 0 sided laminate.  For instance:

4 layer can be made by:

2 side | 0 side | 2 side
1 side | 2 side | 1 side
1 side | 1 side | 2 side

...

5 layer can be made by:

2 side | 1 side | 1 side | 1 side
2 side | 0 side | 2 side | 1 side
2 side | 1 side | 0 side | 2 side

...

6 layer can be made by:

2 side | 0 side | 2 side | 0 side | 2 side
...

The only down side to odd numbers of layers is the supply house
has to stock 1 sided laminate.

-Chuck Harris