Re: gEDA-user: wacky (or not?) solder stencil ideas
John E. Perry wrote: > [EMAIL PROTECTED] wrote: >> ... >> 2) Slap it in the laser cutter, and print the paste layer on it with >> just enough laser power to blast away the blue paint. (The CO2 laser is >> the wrong wavelength for cutting metal, it just reflects off.) >> > > The CO2 laser is the standard tool for metal cutting. Particularly in > very high power applications, I think the key phrase here is "very high power" -- which is not what I have access to. ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: wacky (or not?) solder stencil ideas
[EMAIL PROTECTED] wrote: > ... > 2) Slap it in the laser cutter, and print the paste layer on it with > just enough laser power to blast away the blue paint. (The CO2 laser is > the wrong wavelength for cutting metal, it just reflects off.) > The CO2 laser is the standard tool for metal cutting. Particularly in very high power applications, it's much less expensive to build, and where the metal is not perfectly adapted to the CO2 wavelengths, a "helper gas" such as oxygen does the adaptation very well. http://www.synrad.com/fseries/index.htm http://www.hackaday.com/2005/03/27/cut-sheet-metal-with-your-homemade-laser/ http://blog.makezine.com/archive/2005/03/100_watt_metal.html http://www.e-lasercutting.com/ http://news.thomasnet.com/fullstory/27568 http://www.e-lasercutting.com/ John Perry ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: wacky (or not?) solder stencil ideas
> Dave wrote: > > and paint both sides with "machinists' blue stuff" -- I'm > not sure what it's properly called Prussian Blue. Though not the neo-nazi/white-power rock band. > > The CO2 laser is the wrong wavelength for cutting > metal, it just reflects off.)> The CO2 laser will cut metals. Just not ones like copper and brass. ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: wacky (or not?) solder stencil ideas
DJ Delorie wrote: > For my sized boards, I usually end up with one web etched through > somewhere and one hole elsewhere not etched through. Same deal with laser cut mylar. I just tweak and recut until I get something that works. For TQFP, I make the pads very narrow since they bloom due to combined beam kerf and meltage, that preserves the webs. Then tweak the laser power until I get clean web everywhere, and clean up any incomplete apertures with an X-Acto. > >> I've tried 65# card stock, mainly because it was handy. Too thick >> for a stencil, 40# might be about right? > > 20lb is 4 mil, just right. > >> I'm concerned about contamination from carrying ash residue >> into the solder joint. > > Flux should fix that? I'm no chemistry whiz, so if that's true I'd like a smarter person than me to tell me so :) If a residual amount of paper ash is not going to contaminate the joint, then a paper stencil might be an excellent option. -dave ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: wacky (or not?) solder stencil ideas
> Actually, TechShop is gearing up for franchising. By next year this > time, you, too might have a TechShop close by. Warning: time sink > ahead. :) Are you kidding? I don't even have a Starbucks nearby. Not that I wouldn't mind opening a TS franchise, but I don't think there's enough market for it around here. > No, I believe they are YIG laser. Ah. > Does the undercut really make the stencil unusable? It makes the stencil more... unpredictable. The shape of the sides means that the masked side must be towards the board (else the angled sides won't release the paste), so the "hole" size is always going to be bigger than the actual resist opening. Thus, you have to shrink the resist by some fraction of the thickness of the foil, the fraction depends on the etch technique (different techniques have different amounts of undercut) and the precision of your plot. http://www.delorie.com/pcb/brass/20070221-60-top.jpg For my sized boards, I usually end up with one web etched through somewhere and one hole elsewhere not etched through. > What kind of photo resist? Got a pointer? Any kind of dry-film resist should do. > I've tried 65# card stock, mainly because it was handy. Too thick > for a stencil, 40# might be about right? 20lb is 4 mil, just right. > I'm concerned about contamination from carrying ash residue > into the solder joint. Flux should fix that? ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: wacky (or not?) solder stencil ideas
DJ Delorie wrote: >> Yesterday while I was at the TechShop experimenting with the laser >> cutter > > You suck ;-) :) Actually, TechShop is gearing up for franchising. By next year this time, you, too might have a TechShop close by. Warning: time sink ahead. :) Yesterday they were checking out the latest new tool. A CNC hot wire foam cutter... that accepts 8 foot by 8 foot by 10 foot blocks of foam. Wanna kayak? Print one. > >> 2) Slap it in the laser cutter, and print the paste layer on it with >> just enough laser power to blast away the blue paint. (The CO2 laser is >> the wrong wavelength for cutting metal, it just reflects off.) > > Huh? I thought CO2 was what they cut metal stencils with. No, I believe they are YIG laser. CO2 just reflects off, the wavelength is about 10x what you need to cut stainless or other shiny metals. CO2 is great for cutting and etching wood and acrylic. The big market is trophy and corporate awards shops. CO2 does a very spiffy job on balsa wood if you are into modeling. I do a lot of acrylic for robot chassis and other widgets. Shameless plug: www.bowcritter.com > >> Anyway, DJ, I've looked over your web site where you do basically this >> with the toner transfer method. Got any comments? > > The trick to etching paste masks is to etch from both sides to reduce > undercut. That means careful alignment of both sides, which is tricky > with toner transfer (mostly because you can't see through the paper to > align it). Otherwise, the mask'd side is undercut by N mils, where N > is the thickness of the foil. Does the undercut really make the stencil unusable? Or is it something you can live with? Flipping a sheet of brass over on the laser cutter is probably not possible to do with sufficient precision. I've done some tight tolerance positioning by building fixtures, but I'd never be able to flip a sheet of brass and put it down withing a couple of mils. > > The best method I've seen so far is to take generic aluminum foil, > laminate a photoresist on both sides, and expose/develop. Now, DIP it > in FeCl - the aluminum etches almost instantly. Use as-is - don't > strip the photoresist! The combination of foil and resists is just the > right thickness for solder paste stencils. What kind of photo resist? Got a pointer? > >> Topic two: I've been trying to get a process that makes stencils in 3 >> mil drafting mylar. > > Have you tried plain old 20lb copy paper? I've tried 65# card stock, mainly because it was handy. Too thick for a stencil, 40# might be about right? It cuts very cleanly. Very nice looking mask. Nice and sharp and repeatable. And not tweaky to cut. Unfortunately, cutting paper creates a thin scorch area at the edge of the cut. I'm concerned about contamination from carrying ash residue into the solder joint. > >> Third wacky idea: TechShop has one of those PCB mils. > > I've seen someone do it with just a CNC drill - one drill hole for > each pad, leaves a spot of paste. Won't work for TSSOP, but will for > 0603 et al. > > For fine-pitch parts, it's almost easier to etch a slot along the pins > and rely on surface tension to put the solder where it's needed. Makes sense. -dave ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: wacky (or not?) solder stencil ideas
On Feb 15, 2008, at 2:36 PM, Dave N6NZ wrote: > Yesterday while I was at the TechShop experimenting with the laser > cutter and talking about solder stencils with other folks, this idea > came up: *grumble*...living in a gorgeous area but it's a technological wasteland...*growl* > 1) Take 3mil brass sheet, and paint both sides with "machinists' blue > stuff" -- I'm not sure what it's properly called, but it's a blue > paint > that they put on metal so that they can scribe layout marks. It's called "layout dye", FYI. > 2) Slap it in the laser cutter, and print the paste layer on it with > just enough laser power to blast away the blue paint. (The CO2 > laser is > the wrong wavelength for cutting metal, it just reflects off.) Initial reaction...As someone who has worked with high-power lasers in a previous life, the last thing you want is laser light reflecting around...especially IR light from a CO2 cutting laser. That's so dangerous I don't even want to think about it. -Dave -- Dave McGuire Port Charlotte, FL ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: wacky (or not?) solder stencil ideas
> Yesterday while I was at the TechShop experimenting with the laser > cutter You suck ;-) > 2) Slap it in the laser cutter, and print the paste layer on it with > just enough laser power to blast away the blue paint. (The CO2 laser is > the wrong wavelength for cutting metal, it just reflects off.) Huh? I thought CO2 was what they cut metal stencils with. > Anyway, DJ, I've looked over your web site where you do basically this > with the toner transfer method. Got any comments? The trick to etching paste masks is to etch from both sides to reduce undercut. That means careful alignment of both sides, which is tricky with toner transfer (mostly because you can't see through the paper to align it). Otherwise, the mask'd side is undercut by N mils, where N is the thickness of the foil. The best method I've seen so far is to take generic aluminum foil, laminate a photoresist on both sides, and expose/develop. Now, DIP it in FeCl - the aluminum etches almost instantly. Use as-is - don't strip the photoresist! The combination of foil and resists is just the right thickness for solder paste stencils. This works because the foil is so thin you can just pre-align the two mask prints (which is easy because they're transparent), then slip the foil between them for a near-perfect alignment. > Topic two: I've been trying to get a process that makes stencils in 3 > mil drafting mylar. Have you tried plain old 20lb copy paper? > Third wacky idea: TechShop has one of those PCB mils. I've seen someone do it with just a CNC drill - one drill hole for each pad, leaves a spot of paste. Won't work for TSSOP, but will for 0603 et al. For fine-pitch parts, it's almost easier to etch a slot along the pins and rely on surface tension to put the solder where it's needed. ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
gEDA-user: wacky (or not?) solder stencil ideas
Yesterday while I was at the TechShop experimenting with the laser cutter and talking about solder stencils with other folks, this idea came up: 1) Take 3mil brass sheet, and paint both sides with "machinists' blue stuff" -- I'm not sure what it's properly called, but it's a blue paint that they put on metal so that they can scribe layout marks. 2) Slap it in the laser cutter, and print the paste layer on it with just enough laser power to blast away the blue paint. (The CO2 laser is the wrong wavelength for cutting metal, it just reflects off.) 3) FeCl etch. The blue stuff is a resist. You now have a paste stencil. Anyway, DJ, I've looked over your web site where you do basically this with the toner transfer method. Got any comments? Topic two: I've been trying to get a process that makes stencils in 3 mil drafting mylar. I've got a usable stencil with relatively fine-line parts, but it was more than a little tweaky. There is a fine line between cutting through and getting goo because the material is so thin and prone to melt and stick to itself. I ended up printing three the paste layers with 3 different bloat settings, converted all of them to dxf, and merged the drawings and cherry-picked the "best" image for each footprint. I see where Grafix makes essentially the same material as drafting mylar, but coated with a "secret sauce" specifically designed to keep it from sticking to itself when laser cut. I need to get hold of some samples of that. It looks like they have a $100 minimum order on this material. I'm guessing that Pololu and the other places that cut cheap plastic stencils for you are using this stuff. Third wacky idea: TechShop has one of those PCB mils. I suppose you might do a stencil in sheet brass with it, but I'm not sure it can cut a fine enough line. I need to find out the specs. Comments? Ideas? -dave ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
