Prototyping Surface Mount Components??

You might be surprised what is possible, with just hand tools. A fine-point soldering iron, and one of those illuminated desk magnifiers, will take you quite a long way. Tweezers to position components. Most packages except BGAs can be done this way. You'll find solder paste easier to use than solder wire, as things get smaller. Even BGAs have been done at home, using an oven or (horrors!) a toaster. But this is definitely an advanced technique. As to programming, don't consider a CPU that cannot be reprogrammed in situ. Most modern CPU's can be programmed (often debugged also) via a JTAG port, or the like. Always provide for this in your PCB layout.

For PCBs, I have given up making them at home. A local fab shop offers a really good price for prototypes, if you don't need them yesterday. (He waits till he can fit them in the corner of a panel that's going through anyway.) The finish, accuracy & general quality saves me so much stress in putting it together.

I would go a little further and suggest a low-power microscope for under $100. For 58 year old eyes, I need all the help I can get.

Besides JTAG, there are vendor-specific In Circuit Serial Programming connections, like the 5-wire connection used on Microchip parts. Low end micros are more likely to have these than JTAG.

Robert Scott Ypsilanti, Michigan

David R Brooks wrote in news:446af366$0$26936$ snipped-for-privacy@per-qv1-newsreader-01.iinet.net.au:

Solder paste is overrated. :) Joke, but there's a serious point to it. To solder a chip with two rows of very fine pin spacings on each end, I've used a normal iron and solder. I tried all sorts of things at first, then found that the old way works better by far than anything you'd expect to use with SMT. The trick is to keep the tip very clean, apply the solder liberally, and use gravity and cohesion on the iron to draw the solder away as you move along the row. This leaves shiny joints that are not starved, and a bit of fluxed braid can remove the solder bridge that is usually left on the last two or three pins, and if you get it right you won't even need to do this.

Close viewing is vital, it will show you the results of your technique in merciless detail. >:) I've found that the same idea is good for SOT23 and various tiny capacitors and resistors, I place the acute angled edge of the tip against the PCB, just clear of the part with the flat of the tip facing it, make a small bead of melted solder there, then quickly bring it to the part and back away, and the resulting flow makes a very neat raised fillet. I anchor the part with a tweezer or jewellers screwdriver for first contact, then do the other end properly as I decribed, then finish with proper flow to the first end.

In all cases I've found that the best way to get good SMT contacts is to use plenty of solder, not to worry about too much heat, because this is the way to make the contact fast. Being fast is a better way to avoid excess heat than trying to reduce the amount of hot solder.

I do have quite a bit of waste solder collected though, over the years.

I have just moved to in circuit programming of a SMD PIC, in the past I made many boards using a DIL package PIC in a ZIF socket, pulling it for programming in a separate programmer. Having used ICSP once I can't say I'll ever go back, the coding/testing cycle is just *so* much less hassle with ICSP. Way to go!

Don't be afraid of using SMT components, you don't need much equipment at all, I make my boards at home, no fancy tooling at all. A stereomicroscope is very useful, it makes life a lot easier, though you can do the bigger SMDs by eye alone. They can be had relatively cheaply. You will need some layout software, a decent printer, a UV lightbox, some pre-coated photo board, a tray of developer and of etch. You can solder with a fine iron and solder (0.4mm is good), or use paste, but paste is not essential at all. I work with 8 thou tracks routinely using a standard inkjet for output, I print masters on tracing paper which works well, you don't have to use film. Double sided is easy to do using the stapled pocket method, just line up the two masters (ink inside) first and staple together, sliding your unexposed board between them.

I'm using a Microchip ICD2 for programming the PIC, this comes with a RJ12 output lead, you just need to add a SMT RJ12 socket to the board and you get a really neat programmer connection.

Steve

For the Atmel AT91RM9200, they have an onboard serial bootloader that be activated based upon a jumper, so the programming of your board is done in-system. To program it, you will need a serial port on your PC, a terminal program like minicom or hyperterminal and off your go.

However, I would recommend you get one of Atmel's eval board, either the DK or the EK. I have had very good experience with the DK eval board, and it certanily reduce our bring up time on the whole project.

I have not used a bootloader before. I would assume it is straight forward to load the new program after you get the serial port up and running. Am I correct?

Yes, I am thinking of getting one of these if I can come up with the money to do so. Does anyone have any recommendations of good evaluation kits for the AT91RM9200?

[snip] [snip] [snip] Whatever works for you :) I have tried paste & wire, and I prefer paste. Just my $0.02

Not on this chip. The bootloader can only download code to the internal SRAM (16KB but can only use about 12K download size) and start that. Usually you will load a small loader program that sets up memory etc., downloads the real code and programs it to flash. The loader can use the internal ROM services, so doing an X-modem download is very easy. I believe the eval kit comes with samples of this but you should also be able to find something on the internet.

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Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

David R Brooks wrote in news:446c4864$0$26942$ snipped-for-privacy@per-qv1-newsreader-01.iinet.net.au:

I had a hell of a time trying to get all the paste to melt, had to clean up a load of unmelted goop and start over. Fluxed wire and a standard tip worked very well. I already decribed how to do it so I won't repeat it. :) The results are extremely good though, before I did it I had some terrible things to contend with.

One nice example was the poor heat conduction with paste or inadequate solder by wire. I overheated a track on a tiny row of 80 IC pads, and it was dragged by the iron, half turned around its axis. The easiest way to repair was turn it fully over, scrape and tin the other side, then use a needel tip to align it and flatten it ready for the IC replacement. That worked, but it was a nightmare task, by far the most delicate bit of 'surgery' I have done. Making easy contact by lowing a generous bead of solder from a fluxed wire is a good way to avoid anything like that happening. It's also the cheapest way of amking sure that no solid ever comes into contact with the work, risking damage to it while applying solder. As solder flow is uased in commercial manufacture, it makes good sense to use the same machanics on a small scale to get good contacts made.

I still keep paste, I'll probably want it to make small SMT layouts where I heat the whole board carefully to join all parts in one operation, but I don't like it for small repairs. You can't melt it with an iron tip easily, because the flux melts vigoruously, carrying the metal powder away too rapidly to allow melting and cohesion. All that results is a mess that needs cleaning up. That same standard tooling gets good results with wire though.

If anyone reads this and wonders, just try it. :) Try both, and if you post about a way to use solder paste with a stanard iron on a cold board without damage to pads or parts, I'll read it and try it, but without that, my own experience will convince me more than anything else.

As Brooks pointed out, these days a PCB fabrcation house can do it at a lower cost than you can at home.

*-*-*-*-come-and-go-*-*-*+pcbcart+long-term-relationship+slow+batchpcb+waive+barebonespcb+Shanghai+PCBex+*-quality+futurlec

If your time has no value and you want to try it for the experience, Mike Harrison's site has lots of DIY details: http://66.102.7.104/search?q=cache:iiE5D2h-NyYJ:

There is a Yahoo group on this subject:

The lowest cost DIY method is the glossy clay-covered paper method described most thoroughly by Tom Gootee. Short version:

't-use-*-steel-wool+JetPrint+darkest-*-settings+pinholes+zzz+stabilize+acetone+detergent+*-*-sheet-of-regular-paper-*-*-*-*-*+edge+toothbrush+clothes-iron+removal-problems+long-soaks+hot-water+180-*+toner-transfer Long version (He has other cheap tricks here too):

Lower cost? Some copperclad, a sheet of Press-n-Peel or glossy paper and a few cents worth of etchant and toner does not add up to $33+. I could 'pay' myself twice the minimum wage and still be ahead.

Tim

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Did I really still have that sig?

Sorry to hear you're only making twice minimum wage.

You're not factoring in that the 1st time it's not "a few cents worth of etchant"; you have to buy an entire bag or a whole jug (+hazmat shipping ?). You also didn't mention the basin. (Most experienced folks would heat the solution; Harrison rig shows a Pyrex dish.)

Surface prep, ironing, remove PnP, inspect, correct flaws in toner deposition, mix etchant, heat etchant, etch[1], drill for non-SMT items[2], remove toner, inspect, clear flaws, dispose of (or re-bottle) etchant, clean up work area.

It may be a breeze the 2nd time; the 1st time, it's a good chunk of a day consumed. If you're using clay-covered paper, add even MORE time.

The 1st time is where you learn all the little tricks and most folks don't want to do it themselves a 2nd time. . . [1] If you don't have a mechanical agitation system, you have to stay close by and do it manually.

[2]The whole *vias/PTHs* thing is a discussion all unto itself.

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I don't recommend it but at Tektronix in 1989 I had zero budget, available time, a 750 Mhz counter timer, and desperately needed to demonstrate higher frequency applications with this.

So I begged a few 2.8Ghz divide by 4 parts from one of the vendors, got a postage stamp sized bit of double sided clad circuit board, got out the dremel tool, and went at it.

The divider was only 8 pins on .05" centers. I only needed a few surface mount resistors for termination. And I only had a single signal in and signal out peltola connector.

With a very calm morning, a very steady hand, a very tiny dremel bit and a few scrapped boards the prototype was built and worked.

I don't recommend it, and I wouldn't even consider it on any of the REALLY fine pitch parts I see today. But if I only had a few pins I might try soldering short bits of wire wrap wire onto the pins and connecting those to the destination. "bo bo" wires are always fun.

Don't try this with 940 pins :)

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(Just for the sake of accuracy, and maybe more "completeness", for people who might need to decide what the best way to go about getting a pcb made is, in their particular situation:)

The etchant CAN be dirt cheap: I now use two parts common 3% Hydrogen Peroxide plus one part common Muriatic Acid (i.e. 20-something% Hydrochloric, IIRC), which are both very-widely available, in small quantities, very cheaply. [Using a fresh batch, each time, it's less than $0.25 per board; maybe way less.]

It etches a 1oz board at room temperature in about five minutes, with hand agitation (i.e. a hand in a disposable latex glove, gently wiping surfaces of PCB with a small wad of paper towel). [Less than $0.10 per board.]

I etch in a cheap plastic food container from WalMart: [Less than $1. Divide that by the number of boards etched in your lifetime.]

Copperclad, even pre-cut to specs, within .01", is extremely cheap, from the right vendors. [Certainly less than $0.50 per board, for, say, 4"x6" or 9"x3", 1 oz, 2-sided, .082"; and WAY less for cutting/sizing to specs within +/- 1/16".]

Surface-prep requires an abrasive nylon pad (e,g, a "Scotchbrite" pad). [Reusable for at least 20 boards: Less than $0.10 per board.]

I don't use "Press-n-Peel" (PnP). It's just one more thing that I can't get locally within 10 minutes, and is kind of pricey, too. I run glossy inkjet paper through an old laser printer. Even in very small quantities, I think it's less than $0.10 per sheet. (And you can buy a whole truckload of old laser printers for $50.) My old LaserJet 4's toner is super-expensive, around $80 or more, for something like 4000 sheets printed. Assuming only one board's patterns are printed per sheet, that's about $0.02 per board.

And I don't believe that using clay-coated (i.e. "glossy") paper would take MORE time than PnP, even for 1st-timers. Not at all. And I think that the results, using glossy paper, are AT LEAST as good as those with PnP.

The TOTAL time required COULD be as short as 20 minutes from "pattern on computer screen" to "start soldering components", for simple boards (i.e. with very few drill holes; Surface mount would be even better.).

Drill bits: I use used, "re-pointed" carbide bits, purchased in quantities of about 100 at a time for about $25.00. If my drill press (and my technique) don't break too many, we can probably say way less than $0.25 per board.

Well, I probably forgot to mention some of the replenishable materials' costs. But you can probably see the trend and do the math.

For anyone who wants a prototype or one-off PCB, or even a small production-type run, my method is obviously way less expensive, even just in terms of out-of-pocket expenses, even (or maybe especially) the first time.

Each person (or their company) would have to calculate their own time's value, to them or their company, to see if a board-house makes more sense, at that time, for their needs and their situation. HOWEVER, if you need a pcb or two, VERY QUICKLY, e.g. if an engineer's or technician's time is going to be more-or-less wasted until the board is in hand, then you had better also take that cost into account. Delays can be detrimental or costly in many other ways, too. So you might also have to compare the cost of the time spent doing a toner transfer pcb to the large "express turnaround" fee that a board house would sock you with, and then still take a day or more to get your pcb to you, plus the cost of that delay.

Regarding the "1st time" or startup costs, and the extra time required, etc: Most of the costs were covered above, except, of course, for things like driving to supplier locations (or ordering on-line), which also takes some time (and money), as well, plus the "opportunity cost" value of a person's time.

You are probably correct about investing a whole day (or at least a half-day), the very first time you attempt to make a toner transfer PCB. (And if someone is setting up to be able to make small production-type runs, it might be longer yet.)

BUT, hey! How does that compare with the 1st-time costs, and cost of time spent, when using a PCB-fab vendor?? Worst-case might be someone who's never done either method. Are you going to take into account the cost of the pcb-design software they would need, and the time to learn it, to be able to generate the files required by the pcb-fab guys? (Toner transfer files could be created with MS Paint; probably very quickly for small or simple boards.) Even for those already owning, and experienced with, pcb-design/layout software, just finding a pcb fab house to try, reading their website, readying the files to send to them, emailing them, getting a quote, arranging and sending payment, etc, etc, would probably eat up a good half-day, and maybe more, especially the first time. (And, for those people, the artwork for toner transfer might already be done and ready to print.)

You are certainly right about plated-through holes, and vias, being a HUGE problem, for all DIY pcb-making mehods. It uses up a lot of board space, to have to make pads on both sides, for example, for each via. And then a wire has to be soldered through them (or special eyelets crimped in). And I do greatly-dislike not having plated-through holes. If I use, for example, a DIP socket on the top side of a board, then I basically HAVE to approach every one of its pins with a bottom-side trace (or make a "via" pad nearby), or else they can't be connected by soldering. And if board real-estate is getting tight, all of that can be a REAL pain.

SO, it should be noted that, if making a choice between DIY pcb-making and using a board house, then the PCB LAYOUT, itself, would have to be compatible with DIY limitations, for DIY to even be an option. For existing board layouts that were intended for professional manufacture, DIY is not likely to be an option, without re-layout work, except for the simplest of boards.

And, of course, most people limit DIY pcb-making to single or double sided boards. SOME people do make "multi-layer" pcbs. But they generally just use very thin pcb stock and then glue the layers together. Seems like another "can of worms", and more "hoops to jump through". Never tried it, although I have been very tempted, at times.

OK. Sorry to have blathered-on for so long, about all of that!

I hope I didn't sound too biased, and that I wasn't actually unfair or inaccurate in my comparisons, et al.

The bottom line is that I think that, in general, there might be times when DIY toner transfer pcb-making could make more sense than out-sourcing, and wanted to try to shed some light on some more of the factors that might be involved, for someone who might be faced with choosing among the available methods for coming up with a printed circuit board.

(Whomever mentioned my website, in this thread, thanks!)

Regards,

Tom Gootee

tomg at fullnet.com

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It sounds like you get paid over twice minimum wage in your spare time! I wish I was that lucky. While I earn over twice minimum wage while at work, I get paid nothing while I'm not.

Tim

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Did I really still have that sig?

it is a good idea to factor in that while you're waiting on the prototype boards to arrive in the mail you're sitting there "getting paid" to do nothing. sure, we all have other things to do and can occupy our time writing invoices or something, but what we're really doing is wasting time waiting for prototype boards so we can get back to the "real work". the best reason to make boards is because you can have them in an hour (or a few), and in terms of labor costs it's cheaper to pay someone 200$us/hr for a few hours to make a 30$us board than it is to pay someone 200$us/hr to sit around tinkering for a few days waiting for boards to arrive.

as far as i am concerned tom said it all right here, at least in spirit if not in word. the key reason to do your own pcb's is so you don't have to wait around for them to be mailed. it would have probably been cheaper to have pcb's made in the "old days" when everything was DIP too ... but who would do that ? why didn't everyone order their pcb's then ? it's not because they couldn't, or because nobody was around to make pcb's. the reason was because there wasn't a market for them, because it isn't hard to get a through hole prototype board and solder some chips on it, or use wire wrap. the reason it isn't done now is BECAUSE IT IS MORE DIFFICULT, and people don't want to go to the trouble of etching their own surface mount boards.

OR ... you need multi-layer boards and it might not even be feasible to do those yourself. that is a valid argument to make.

if there was some brilliant magical way to just pr> jeffm snipped-for-privacy@email.com wrote:

JeffM wrote: [snip]

't-use-*-steel-wool+JetPrint+darkest-*-settings+pinholes+zzz+stabilize+acetone+detergent+*-*-sheet-of-regular-paper-*-*-*-*-*+edge+toothbrush+clothes-iron+removal-problems+long-soaks+hot-water+180-*+toner-transfer

i used this method.

i think tom's page makes it sound even harder than it really is, and even he makes it sound easy. i believe he was afraid that people would not believe this worked so he went to great pains to be very careful about how he laid out his directions to insure that the people using the method would get the same results that he was getting. truth is, i found i could cut corners even on his easy procedures and STILL get a terrific result. the key thing about this method seems to be making sure you don't rush the part with the iron, that is, insuring that you really do pass the iron over every part of the printed image and really pressing down on it hard and letting it heat up enough to transfer the image. but some of the things he talks about such as the trouble of getting the paper off, etc, i found to be very easy. for me just putting the board under water when i was done was all it took, the paper just came right off in one whole sheet, i didn't have to fight with it at all.

this method is terrific. the only limitation i found with it so far is that in the resolution of my printer! or maybe it's really the resolution of my software. i can't seem to make traces small enough for one of my surface mount chips, the pins are just too close together. for 99% of chips i don't think this is a problem. my other limitation is my own knowledge of pcb layout and my own experience level, which is very inexperienced. more experience with the layout software would probably even solve my problem with the resolution.

but inexperience or no, i have successfully etched boards with this method and it worked great. just for fun i even printed a picture, a photograph that is, in black and white, and transferred that to a copper board and etched it, it turned out really pretty! lol.

the best thing about tom's method i think is the speed. you just print the image, go out and prep your board and use the iron to transfer your image over to the board, clean the paper off, etc, mix up some acid, get your gloves, etch the board, and clean it up. i mean what could be better than that ? it takes basically no time, is easy, cheap, etc, you get your board done and get back to working. and if that board is screwed up, fine, print another page and do it again. that's the beauty of it ... the key word in the phrase "rapid prototyping" is ... RAPID ... lol.

It's your choice: a couple or four hours work, with big inaccurate holes, coarse or broken tracks, and the task of joining the two sides, a bit of gardening between the 0.5mm pitch pads, an age debugging the board, and a low PCB cost. Or 10 days wait and a board with the holes drilled accurately, 0.3mm/ 6 mil rules, PTH, pads accurate, tinned, knowing that the bugs are all your own, at a cost of a couple of hours work at (cheap) engineer's rates, or say four hours at technician rates. Maybe 10 hours at shelf- stacking rates.

Paul Burke