Double sided but not... [Now a review of my new PCB Fab in a Box kit! pg 2]
photomankc
Posts: 943
I'm working on a board for my thermostat project that will actually be a stack-on module to add to the Propeller Platform. When I investigated the cost to have it run I decided that I would probably prefer to get the PCB fab in a box kit and run my own. If I ask for the kit for Christmas and buy the laminator myself I'm looking at the same cost really.
Anyway one problem came to mind last night as I was looking over the board. I was routing in ways that were perfectly great on plated-through holes but that were going to be a problem without that. There are two difficult items. One is the DIP sockets. I have connections top and bottom so that rules out the cheapo CrapShack style. I was thinking that machine pin types might let me get the top side soldered as well but I'm not sure. I could get around that by soldering the chips directly to the board but the SSRs were expensive little guys and I'll never get them back off if they are soldered on both sides. Next is the pin headers that will carry my buttons, LEDs, and LCD to the top surface of the enclosure. I also very much need to be able to solder both sides of those or I'm looking at totally ripping up and starting over. I have added a few SMT parts that I plan to hand solder looking to help reduce the number of holes to drill so I really want to avoid adding vias everywhere to solder wire between layers.
Is there a way most people handle getting parts like that soldered on both sides? I was thinking I could use some wire under the parts to hold them up just high enough to get my small tip under them and reach the pads and hopefully not melt everything in the process. Solder paste comes to mind but having never worked with it it would mean some learning and at least a toaster oven and timer as I understand it. I would think that would still need something to hold the through-hole parts up so they don't drop right down into the solder.
Post Edited (photomankc) : 12/31/2009 11:01:20 PM GMT
Anyway one problem came to mind last night as I was looking over the board. I was routing in ways that were perfectly great on plated-through holes but that were going to be a problem without that. There are two difficult items. One is the DIP sockets. I have connections top and bottom so that rules out the cheapo CrapShack style. I was thinking that machine pin types might let me get the top side soldered as well but I'm not sure. I could get around that by soldering the chips directly to the board but the SSRs were expensive little guys and I'll never get them back off if they are soldered on both sides. Next is the pin headers that will carry my buttons, LEDs, and LCD to the top surface of the enclosure. I also very much need to be able to solder both sides of those or I'm looking at totally ripping up and starting over. I have added a few SMT parts that I plan to hand solder looking to help reduce the number of holes to drill so I really want to avoid adding vias everywhere to solder wire between layers.
Is there a way most people handle getting parts like that soldered on both sides? I was thinking I could use some wire under the parts to hold them up just high enough to get my small tip under them and reach the pads and hopefully not melt everything in the process. Solder paste comes to mind but having never worked with it it would mean some learning and at least a toaster oven and timer as I understand it. I would think that would still need something to hold the through-hole parts up so they don't drop right down into the solder.
Post Edited (photomankc) : 12/31/2009 11:01:20 PM GMT
Comments
www.expresspcb.com
If you decide to make your own PCBs at home, think about what you are going to do with all the nasty chemical waste you must dispose of.
hope that helps,
Mark
I keep looking at the hobby PCB houses but in almost every case they double the cost of the whole project if not triple it. I'd rather point to point wire it in that case and design a prototype board for the Prop Platform that suites my needs better than the present version on Gadget Gangster. At least there the other 2 boards would be useful where for this they would simply be waste.
I'm still confused. Are you saying that the legs of your IC sockets should have gone through the board so they would be solderable to traces placed on both the top and bottom of your board?
Keep in mind that, depending on the size of your projects, you might be able to design 2 or 3 separate projects onto a single PCB and only use the traces you need. So even though you'd have 3 boards of identical design, they could be made quite versatile if you plan ahead.
http://forums.parallax.com/showthread.php?p=827563
You can create "vias" by using a piece of wire and solder on top and bottom as needed. Since it is just wire, you have access to solder both sides
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Andrew Williams
WBA Consulting
WBA-TH1M Sensirion SHT11 Module
Special Olympics Polar Bear Plunge, Mar 20, 2010
Many years ago when we used to make our own boards, we used to use machined pin sockets and solder them both sizes. I suspect it will work, but it's been a lot of years, so I need to try it and find out.
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If you always do what you always did, you always get what you always got.
ETA:·Well, it's doable.· Not something I would want to do very often but it's workable in a pinch.· I would probably need to do the headers first since the angle needed to get under them is so low.· Any parts on the edges will interfere.
Post Edited (photomankc) : 11/11/2009 3:34:54 AM GMT
As far a pulsar's stuff, you will need a laminator to get the stuff to stick to the board if I don't miss my guess.
It would be easier to design the boards combined, and send them off. If you can wait, A place like Ourpcb will get a few boards to your door for around $100 in less than 2 weeks.
BTW I use only this kind: they are much better, secure contacts
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Well, you *can* do it with an iron and bit of doweling, but I do have the recommended laminator. Will see how it comes out.
@dMajo, those sockets are always the ones to use. When I was an apprentice I spent about 50% of my time removing the cheap fold-leaf sockets and replacing them with spun machined pin.
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If you always do what you always did, you always get what you always got.
TABLE WAS SUPPOSED TO GO HERE
11:40:02 11/11/2009 - Help con questo schermo
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I obviously have some problems with my process. I got the first side of the board to transfer and etch pretty cleanly. I etched using a small piece of sponge soaked in hot FeCl and the etch was quick, easy and clean. The bottom side I'm having some serious issues with. I get incredibly clean toner transfers, but I've been having problems applying the TRF and having it smudge the tracks.
The board I'm working on is about 4" x 3", and so far I've used 3 Letter sized sheets of transfer paper, so I've got some process refinement to do yet.
I've got some ideas, but I ran out of time today. I've taken a boatload of photos, but they are pretty much all of failed bits of process. I'll keep at it though.
I must admit, the results are getting better, but I'm obviously still not doing something quite right.
One thing of note. I bought a second hand Laserjet 2200D to do this with as my colour LJ2550 does not do suitable blacks. The LJ2200D had a re-filled toner cartridge in it, and my last couple of attempts were after putting a new genuine HP cartridge in it. That improved the toner transfer results considerably.
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If you always do what you always did, you always get what you always got.
At the beginning (from school) I was used to put the pcb in the liquid so you have to go in with hands to take it out and see it it's ok. Now I use a teflon box fixed on a heated vibrator plate (t=50/55°C, liquid level 3 to 4 cm). I am etching the pcb side per side. You put the pcb at 30/45° touching the liquid on one edge and slowly layng down so that there is no air between the pcb and the liquid (the pcb is floating over the liquid) and then I turn on the vibrator. For single sided boards you see from the outside when the process is compleded because the pcb change the color where the copper on the other side is removed. For double sided boards just have a look and when is done repeat the process for the other side. Doing this way I never had problems also on the thinner traces.
Usually I use precoated boards, for smaller simple projects/tests I use positiv20 photoresist spray (I have a lot of 50x50cm and 100x25cm double layer pannels) and UV lamp. As etching moisture I usually use ferric chloride because of easier handling (I am able to buy also already liquid) and greater efficiency, when I have much parts and time is an issue I use hydrogenperoxide+hydrochloric (muriatic) acid [noparse][[/noparse]parts:2/5/5h2o] (much quicker etching but saturates much before)
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Post Edited (dMajo) : 11/18/2009 2:27:48 PM GMT
I use pre-coated boards, and a home-made UV exposure unit. Artwork is printed on JetStar Premium film with a cheap HP DeskJet printer.
Leon
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Amateur radio callsign: G1HSM
Post Edited (Leon) : 11/18/2009 3:21:09 PM GMT
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If you always do what you always did, you always get what you always got.
www.leonheller.com/Propeller/XProp/XProp_photo.gif
Tracks are 10 mil, I can go down to 8 mil if necessary. I have actually done 5 mil as an experiment on a test board.
Leon
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Amateur radio callsign: G1HSM
Post Edited (Leon) : 1/3/2010 10:30:59 PM GMT
It also turns out I *was* overstretching the TRF, and I still did a tiny bit right at the very end of the board. Next time I think I know how to solve that one. I ended up breaking one track when I got the knife out to scrape a little bit of the toner away as the smudged TRF had created a short.
Both sides of this board were etched with the same 35mL of Ferric Chloride, heated to about 40 Degrees C and applied with 1/8th of a cut up dish sponge. I held the board in one hand and just wiped it slowly with the sponge in the other. Obviously I was not concentrating around the edges as I've left copper on all 4 corners, but those would get trimmed off if I was going to actually use this board.
Unfortunately my registration was off far enough that the board is unusable as I can't reliably solder the top layer where I need to. I'm gonna have to work on that.
The top looks dirty because I used an 8/20 mil crosshatch grid and the TRF was badly smudged. For the bottom I tried solid copper pours, and with plenty of heat in the laminator and real HP toner it was a *lot* better.
The Proxxon drill and carbide bits were worth every cent. It makes it incredibly easy and accurate to drill the board.
Minimum track size here is 10mil, most are between 12 -> 20 and clearances were set to 12.5mil. Even though the board is pretty much toast, I'm not incredibly disappointed for a first ever board.
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If you always do what you always did, you always get what you always got.
I made some tweaks to the layout to increase the clearances, and re-footprinted all the components to give them bigger pads (just to make drilling easier for me). Now I've got the process sorted I can probably live with the old layout, but this one will make the DIP's easier to solder on both sides.
The biggest tweak was to the thermostat in the laminator. I was getting about 130 Degrees C and having trouble getting the toner to stick properly on the first pass. Now it runs at 180 Degrees C and only *needs* one pass.
I solved the double-sided alignment problems by drilling out the alignment holes to 1mm and sticking PCB pins in them. I then just laid the top toner paper on and taped the edges, flipped it over and laid the bottom toner paper on and taped its edges. Pulled the pins out and whacked it through the laminator. I drilled the alignment holes in the board and both toner transfers with my little drill press, so the holes were very clean and pretty close. Check out the through-board photo for a look at the alignment.
I've still got some learning to do, as I did have a jaggy edge on one track. I'm quite confident of 10/10 mil spacings now, and I suspect if I'm not asking the printer to lay down huge slabs of toner it will cope much better with the finer tracks. It was having trouble keeping the density up with the earth planes. Now I've got the procedure right I'll try a hatch pour next time to reduce the amount of toner laid down.
This one took me a little over an hour from sitting down at the desk to scrubbing the board clean and disposing of the etching gear. It will probably take me quite a while to drill though [noparse];)[/noparse]
Overall I'd give the Fab-in-a-Box kit the thumbs up. I'm quite happy with it and now I've got the process working I can start having a bit more fun prototyping.
<edit> Drill took 15 minutes including 3 bit changes.
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If you always do what you always did, you always get what you always got.
Post Edited (BradC) : 11/23/2009 12:24:16 PM GMT
Leon
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Amateur radio callsign: G1HSM
I'm sure they do. I had to use multiple passes too before I modified my laminator. It would appear the more passes you make, the more you smear the edges of the toner. Cheap laminators seem to have difficulty when you ask them to exceed about 160 degrees C.
Photo etch is my next step, when I've got the toner transfer method perfected and I need to go smaller than about 8/8 mil. Remember, this is the first board I've ever done at home, so I've a bit to go yet. I'm sure when I have as many years experience as you do under my belt, I'll have ascended to the next level [noparse];)[/noparse]
You also have to note, I live in the most remote capital city on the planet. It's not incredibly easy to get access to affordable pre-sensitized board. Plenty of good quality stuff you need to pawn a kidney to buy, and some very affordable stuff of incredibly questionable quality. The rest costs a fortune to get shipped in. If I can make the toner transfer method work for me I'll save a fortune using cheap board from china where I don't have to worry about the photoresist quality. The paper is cheap enough and available locally.
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If you always do what you always did, you always get what you always got.
Next time I'll clean the board first and maybe add a little bit of extra flux. The tip on my iron is not particularly small so there has been the odd slip to the ground plane. Nothing that shorted though, it just looks untidy.
No need to space the dip sockets of the board, just pop the iron fairly firmly between the track and the pin and solder.
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If you always do what you always did, you always get what you always got.
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I'll give that one a go, but I have a concern as to how the pad on the top of the board gets heated without direct iron contact. I'd be worried about overheating the pin and damaging the plastic on the socket that retains the pin.
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If you always do what you always did, you always get what you always got.
The headers were easy. Solder the bottom, slide the plastic carrier up the pins, solder the top and slide it back down again.
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If you always do what you always did, you always get what you always got.