Advice needed with SX48 PCBs

Tony Leyland

Hi,

My current project has outgrown the ROM space of the SX28 and I'm therefore developing on the SX48.

I'm now in a position to produce a prototype PCB (1 or 2 units). I'd like to do this myself rather than
use a PCB production company and I realise I could use a Parallax SX48 ProtoBoard, but I enjoy a
challenge and I will be needing to produce other working projects based around the SX20 surface mount
device, so any experience gained will be put to good use !

I'm a DIY engineer, but my company has allocated a budget of $500-$1000 for purchase of any
necessary PCB production tools.

I know this is a little off-topic, but I would like to ask if anyone has experience making a double sided
PCB that can incorporate an SX48 ? I've read with interest in other threads on this forum about soldering the SX48 in
place, but looking at the fine pad spacing and the track width needed, is it at all possible to produce such a PCB
by hand rather than by machine ?

The tools I would be using (but have not purchased yet) will be:-

PCB UV exposure box.
Etching tank

I currently have the following tools:-

EaglePCB
High quality Laser printer (1200DPI) for artwork.
PCB drill + stand

As I say, I'm sorry it is a little off-topic, but if anyone can tell me if it’s possible and point me in the right direction
regarding the suitable PCB exposure/etching tools that will produce the fine detail of the
SX48 pads and tracks, I would be very appreciative.

Thanks in advance for any help.

Tony

Bongo

This topic was delved into in the sandbox, I do believe. In there you can find what has worked for a few different people.

Reproducing tracks small enough for the SX 48 is easy. Reliably soldering a SX 48 onto them is a little more difficult. This has been a topic in itself and I would recommend that you do a search for it. Had some good advise.

I use tracing paper to print the design to and use as a photo mask. Everybody else seems to like some type of transparency. I have had much better results with tracing paper.

Set your printer to 600ddpi. This is good enough for tracks down to 5 thou. Printing at 1200 dpi will increase the amount of heat put into the medium, which leads to distortion. Tracing paper distorts less than transparencies.

For easy hand production I use 30 thou tracks and 40 thou gaps to the solid planes. The wide tracks are less prone to peeling from the heat of an iron,or pressure of a blunt drill bit. And the wide gaps are nearly impossible to accidentally bridge.

Print 1 layer as a mirror (image) Tape the artwork emulsion sides together and slide your board in between. Like a sandwich. Expose, develop and etch. It is easy, bit of practice is all.

I use 1206 sm parts where possible. Meaning thats what I keep for common items like 10k resistors and 0.1uF bypass caps. Saves drilling holes, saves space, better performance from the caps and definitely easier to solder to smaller tracks.

hope this helps

bongo

Javalin

Hi Tony,

I make double sided pcb's boards all the time.

If you're not looking at a volume production, i'd look at the press-n-peal system. Its available in the UK from www.maplin.co.uk:

http://www.maplin.co.uk/Module.aspx?ModuleNo=13464&criteria=Etching Equipment&doy=21m4

For a kit of parts look at:

http://www.maplin.co.uk/Module.aspx?ModuleNo=17352&criteria=Etching Equipment&doy=21m4


I've had good success with this. Have a look in the sandbox forum at this thread:

http://forums.parallax.com/forums/default.aspx?f=15&m=111240

James

Javalin

Oh, btw,

I haven't (yet) done surface mount stuff.

james

LoopyByteloose

While double-sided boards are DIY feasible, you may consider using 3.3volt power to reduce EMI. If you really want a speed demon, use the Parallax SX-48 Proto Board as it is 4 ply.

The 4 ply reduces EMI problems, too.

Still, you may pull the 5v regulator and install a 3.3v to run cooler and quieter. I am not sure if you can locate a 75Mhz osc at 3.3volts though. The 50Mhz resonator will do fine. Maybe I am wrong and Parallax's 75 Mhz oscillator will work, but the specs say +5V.

But, those extra layers are worthwhile.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Post Edited (Kramer) : 4/21/2006 4:17:58 PM GMT

Bean

Tony,
I use and recommend the PCB kit from Pulsar http://www.pulsar.gs/PCB/a_Pages/4_Products/4e_Starter_Kit/Starter_Kit.html
I have made several boards with the SX48 with no problem.

Bean.

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"SX-Video·Module"·available from Parallax for only $28.95 http://www.parallax.com/detail.asp?product_id=30012


"SX-Video OSD module"·available·for only·$49.95·www.sxvm.com
Available now! Cheap 4-digit LED display with driver IC·www.hc4led.com

"I reject your reality, and substitute my own." Mythbusters
·

Guenther Daubach

Kramer said...
While double-sided boards are DIY feasible, you may consider using 3.3volt power to reduce EMI. If you really want a speed demon, use the Parallax SX-48 Proto Board as it is 4 ply.

The 4 ply reduces EMI problems, too....

...But, those extra layers are worthwhile.

I wonder if you have got a special version of the SX-48 Proto Board as the ones I've got are 2 ply only ?

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Greetings from Germany,

G

LoopyByteloose

I make two layers on a Inkjet with Eagle.
I just print out positives and expose the first one.

Then I drill two of the required holes that are diagonally opposite and farthest apart.
[noparse][[/noparse]I use a tiny bit and drill by hand with a Pin Vise -- lots of control for accuracy.]

These two holes are used to line up the second side for exposure.

Bingda... bingda ... Boom!
Tight registration as everything between will have less error than those two holes.

After that is it pretty straight forward.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Rsadeika

Now, I am curious, how can you tell if a PCB is 2 ply, 4 ply, or any other ply. I have never worked with PCB's, so I do not have the slightest idea on how you would determine the ply factor.

Ray

Forrest

Hold it up to the light and look for circuits buried inside the board.

Everyone should really use the correct terminilogy here. A board with a circuit on one side is called a single-sided circuit board. A board with a top and a bottom circuit is called a double-sided circuit board. A board with a top circuit, two middle circuits and a bottom circuit is called a 4 LAYER board, etc.

Ply refers to a layer of resin impregnated woven glass cloth used to construct a circuit board and one ply is typically 0.0035 in. thick, but this can vary depending on the style of woven glass cloth. A double-sided circuit board can contain anywhere from 4 to 25 ply's - depending on the board thickness. But there are only two copper clad layers that form the circuits.

Post Edited (Forrest) : 4/22/2006 5:19:20 PM GMT

Guenther Daubach

Forrest said...
Hold it up to the light and look for circuits buried inside the board....

This is exactly how I found out that my SX48 Proto Boards have two layers only, and I agree with you, "layer" is the correct word here.

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Greetings from Germany,

G

Tony Leyland

I've been looking at the Pulsar TTS (mentioned above) and I must say it looks awesome. No need for development tanks, UV exposure and
etchant tank (if you use the method they suggest). You can apply the usual white component legend and give the board a nice green
protective colour to give the prototype a more professional look.

I'll be ordering the starter kit soon (export edition without the laminator).

Cheers
Tony

Electronegativity

Hi Tony.

I have also had good experiences with the pulsar TTS.
The small circuit board in my avatar is a matchbox sized Simon Says game with an SSOP SX28 in the center.

I would reccommend using fine grade steel wool to clean the board instead of the scotch-brite pad, and doing the green TRF step twice.

You should also buy an etch resistant marker like this one to touch up any areas where the toner fails to transfer:

www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=280708&Row=370950&Site=US

Also invest in some way to "tin" the boards and be sure to use flux when soldering fine-pitch IC's.

Good luck!

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I wonder if this wire is hot...

Bean

Tony,
I always run the green film through the laminator at least twice.
You can use a regular "Sharpie"(R) marker for touch ups.
To "Tin" the boards I use "Liquid Tin" from MG Chemicals.

What do you use to get the green film and toner off the board AFTER it's etched ?

Bean.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"SX-Video·Module"·available from Parallax for only $28.95 http://www.parallax.com/detail.asp?product_id=30012


"SX-Video OSD module"·available·for only·$49.95·www.sxvm.com
Available now! Cheap 4-digit LED display with driver IC·www.hc4led.com

"I reject your reality, and substitute my own." Mythbusters
·

Electronegativity

Hi Bean, I use 100% acetone.

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I wonder if this wire is hot...

Jamesx

Bean and Electronegativity:

These hints look like they've been learned the hard way. But with them, I'd almost be willing to try this Pulsar system.

Got any more helpful hints that makes this process as easy as the web site says it is?

PJMonty

I'm curious why there is such a push to make PCBs yourself. The original poster had a budget of $500 to $1000 to buy supplies. That same amount of money will buy a fair number of prototype boards manufactured at a PCB company. In addition, the prototypes will have plated through holes and vias (and optionally silk screen and solder masks) which is not very likely in the homemade board.

I'm sure that people will say that once the supplies have been bought, the rest of the boards are essentially free. Well, that would be true if no one charges for their own time. Since making the schematic and PCB layout are required no matter who makes the boards, that part can be ignored. However, to make the actual PCBs, you need to create the mask artwork, transfer it to the copper clad blank, etch the board, and drill all the holes. You then have a board with no silk screen layer for parts placement, no solder mask, and your number of solder connections are probably doubled since you now have to solder wires through every via in the board.

If you get paid $20 an hour and it take 5 hours to do all of this, you have spent $100. If you try to add either a solder mask or a silk screen mask I guarantee you the board will take far in excess of 5 hours to make. This adds up in a hurry. I would personally skip all the home brew PCB stuff and just send it out to a vendor. Let someone else deal with the toxic chemicals and all the rest, while ending up with a board that is almost guaranteed to be better, all at a price similar to doing it yourself

Thanks, PeterM

Tony Leyland

Peter,

I agree with you here. I'll explain a little about the reasons for my initial posting.

I'm designing several SX based projects that have a small component count (less than 10 in total
as the software on the SX is large and handles everything) and I'm using SMT devices. The projects
are a small piece of a larger system that we will be selling maybe 10 or 20 a year, but at a high selling price.

I'll need to make 2 prototypes quickly then issue to our beta testers who will be driving around testing
the whole system. Any changes to the circuit design can then be done quickly and re-tested.
Once we make the final product (10 say), I will then send my layout to a PCB house to make.

I therefore need to learn about how to produce PCB prototype boards and I have been interested
in the techniques for years, but not had the chance to do anything about it until now
as circuit design is not really my day job !

I also have to make several SX based tools that I need to make a PCB for, but cannot justify
the costs of a PCB house. From what I've heard here, using the Pulsar TTS system seems to
be the ideal system for my needs.

I'm inspired by the results made by Bean with his SX Video Module in this thread:-

http://forums.parallax.com/forums/default.aspx?f=15&m=76550&g=83373#m83373

Also, in 9 months time I will be moving to Australia (from the UK) so I will be taking all my electronics tooling
with me and working as a part-time consultant to my UK company, as design changes are
needed (new prototypes, software changes etc).

Hope that explains things,

Cheers
Tony

Electronegativity

Hi Peter, My motivation is slightly different.

This is a hobby for me so I like to do as much as possible myself.
Making the PCB boards is part of the fun, and adds to the amazement when I show off the completed projects.

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I wonder if this wire is hot...

Bean

Peter,
90% of the time I make prototypes just to make sure the boards are correct. I can make a board in less than 2 hours, then populate it and test it. It may not look the best with wire through the holes but I can make 3 or 4 revisions in 1 day.
For me it's about turn-around time. Plus as was mentioned above, it's so cool.

I wish I could find an easy way to drill the holes though....

Bean.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"SX-Video·Module"·available from Parallax for only $28.95 http://www.parallax.com/detail.asp?product_id=30012


"SX-Video OSD module"·available·for only·$49.95·www.sxvm.com
Available now! Cheap 4-digit LED display with driver IC·www.hc4led.com

"I reject your reality, and substitute my own." Mythbusters
·

Electronegativity

Hi Bean, I use this along with the X-Y translation table and it works great.
I drilled over 100 precision holes for DIP chips and headers in less than an hour.

www.ares-server.com/Ares/Ares.asp?MerchantID=RET01229&Action=Catalog&Type=Product&ID=81631

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I wonder if this wire is hot...

PJMonty

I definitely understand the desire to learn a new skill. If that's the goal, than go for it. I still feel that if you're doing a prototype board, you're better off letting someone else suck hazardous fumes, but that's just me.

Tony, you mention that you don't have the budget for using an outside vendor. Have you looked at this company:

www.batchpcb.com/index.php

They are a legit company, with a lot of happy customers. The PCBs they make have a $10 setup fee, and $2.50 per square inch for a double sided PCb with plated through holes, and silk and solder masks. The minimum board size is 1 sqaure inch. This means that if you have a tiny board, you could spend as little as $12.50. I don't know how big your boards are, but are you still sure you can't afford it?

Thanks, PeterM

Tony Leyland

Thanks Peter. They look good to me, I will definiately consider them if my own attempts fail !

Bill Franke

I've been very impressed with www.PCBFabExpress.com. They seem to use a thicker copper layer than some of the other fab houses and the silkscreen and soldermask come with it. I've used them three times with perfect results. Competitive prices as well. The drawback is that you will need to come up with a schematic editor that can produce gerber files. I believe there are some free ones out there, though.

Tony Leyland

Just produced my first board using the Pulsar TTS PCB prototyping system and I have to say I'm very impressed with the quality of the
end result. The toner transfer's exactly from the sheet of paper (that came out of the laser printer) onto the copper.
The wording on the component side of the board was ironed on in the same manner.

A board ready for component placement takes easilly under an hour and does not need developer, light box or etching tank.

The etching method they describe (uses a small sponge dipped in Ferric Chloride and then stroke the copper) is nothing short
of brilliant - the single sided test board shown here was etched in less than 5 mins at room temperature. The green etch resist
sheet and toner is then removed with Acetone (nail varnish remover).

For anyone wishing to quickly produce PCBs, for home use or small prototype runs, I'd recommend this system.

I also tried SMD devices for the first time (0805 size) and I have to say I won't be going back to through hole devices ! all
you need is a magnifying light and a small tipped iron.

I'll now be concentrating on producing a PCB based on the SX-48, as stated at the start of this posting. Thank you all for you help.

PS. If anyone wants the EaglePCB layout of this SX-20 adapter as shown here, I'll submit it (if no one has any objection that is).

Bean

Tony,
Nice job. There is just something special about making your own PC boards. I like the marking you did. That is just toner right ?
Bean.

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Electronegativity

Looks great!

You might want to consider tinning the board, since it's supposed to make the soldering a little easier.

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I wonder if this wire is hot...

Tony Leyland

Hi Bean,

Thanks a lot. Yes I agree, it's been an exciting time learning how to produce a board form scratch and then power
it up and hopefully it works !

Yes, its just the toner straight from the TTS paper. Applied in the same way as for the copper tracks etc. I've found that
the toner actually fuses to the glass fibre board and so the black legend is quite tough. If you do remove the toner with Acetone,
it is still visible as it has 'burnt' into the face of the board.

I tried the white film paper (to get that nice silk screen effect found on pro boards), but found that it blured the text too much.
That's why I've used just the toner.

The photo was taken just after soldering as I was about to apply flux remover and I was worried that the toner would come off.
I'm happy to say that after applying it, the toner stayed on completely and the board looks better.


Hi Electronegativity,

I had hoped to use the tin plate method you mention, but my supplier had insufficient stock and has only just
sent it to me today ! I wonder if I could dip the whole board in it now...

All my future ones will be tinned and hopfully make soldering the SX-48 easier.

Cheers
Tony

Bean

Tony,
If you using the "Liquid Tin" it is amazing stuff. It's almost instant. PLEASE wear goggle and gloves the stuff is wicked if it gets on your skin. I always wash my hands and arms after using it, just to be safe.

If you do try dipping the populated board, let me know if it works. I don't see why it wouldn't though.

Bean.

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Cheap 4-digit LED display with driver IC·www.hc4led.com


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Tony Leyland

Ok will do, thanks for the warning.

I've got a full boiler suit, latex gloves and wrap around goggles as well...just in case !

Tony

rcarmel

Hi Tony,

You mentioned sharing the layout design for this pcb.· I would very much like to see it.

Thanks,

Rich