Almost all proto PCBs come HASL solder-plated, and I assume you have to add flux; but how do you get the parts to stick to the board before you put them in the oven? And is the plating enough solder for reflow?
James,
One thing I've noticed with Kapton is that it's a lint magnet. Another trick I've gotten from auto detailers (but have not yet tried) is that perfume-free clothes dryer (fabric softener) sheets, when used as a wiping cloth, will reduce the static charge. I believe they're also lint-free.
Yes I do have to add flux. The flux will hold the parts in place for a short while but mainly i am just very careful not to bump the boards until after the parts have set. I don't have a pick and place machine I have to place each part by hand.
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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
Another option for laser machine may be for soldering. I thought I posted this some where before, but I don't see it in this thread.
I was reading a book on soldering techniques. There was a chapter or two on laser soldering. The book had all sorts of math and science in it and I sat down and read some of it, but not enough to soak it all in. I wonder if it is possible to do this with the desktop machines.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Timothy D. Swieter, E.I. www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT www.tdswieter.com
mctrivia said...
I just get my pcbs made solder plated. They don't charge me anything more and they are ready to go in the oven as soon as i get them and put the parts on it.
Laser engraver would be cool for other things though. So would a 3d printer but I am broke at the moment.
I agree, some PCB manufacturers do put enough solder on the pads to do just this. But I have seen a lot of boards that would leave the joints "dry". It depends on who does the boards, and what type of solder.
By industry standard, there shouldn't be enough solder on the pads to do this. If you ask why, because solder when thick, will confuse the registration cameras in automatic machines. The machines require a perfectly flat, thin, solder finish (if the fiducials are coated).
This is one reason we are starting to ask customers why type of plating their boards have. If solder, we reduce the stencil apertures a lot more to prevent bridging. Gold or Silver doesn't get the same treatment.
I used to include local fiducials in the pastemask layer but don't anymore. I figured they'd be easier to see and more accurate if they weren't pasted. But a recent batch of boards that my fab house panelized included global fiducials for the panel, and they were added to the panelized pastemask layer. I didn't complain, since I thought they might be handy for the assembly house to align the steel pastemask against. But I have no idea what's standard in the biz. People just seem to take what I give them without comment.
I used to include local fiducials in the pastemask layer but don't anymore. I figured they'd be easier to see and more accurate if they weren't pasted. But a recent batch of boards that my fab house panelized included global fiducials for the panel, and they were added to the panelized pastemask layer. I didn't complain, since I thought they might be handy for the assembly house to align the steel pastemask against. But I have no idea what's standard in the biz. People just seem to take what I give them without comment.
-Phil
Phil,
The best method is to keep the solder off. We, who assemble boards, do use whatever is sent, and many do not comment back. We, as a company, try to educate our customers of what is the best method for success.
Most assemblers use vision systems to align boards to the Pick & Place and the stencil printer. Visions systems use contrast to "find" the center of the fiducial. With solder on the pads, the contrast varies from center to edge (rounded surface of the solder), and causes vision system error.
If you ever find a board which is heavily produced (video card, memory chip, etc) that actually has the fiducials on it (many are on the panel edges which have been removed), you will find the fiducial bare, or gold plated. Mass producers know the fiducials must be consistently flat with even contrast on their surface.
It is possible to align a board manually, so even with solder on a fiducial, the boards can be assembled. It just slows the process a little.
Phil, do you think you could retry the application of the paste and take a picture this time? I think you should also try and use a 1/8" piece of plastic. I believe a credit card will be to flexible and cause some of the problems you are seeing. I am definitely considering including a free squeegee with all of my stencils. I think this thread also demonstrates the fact that I should put together a more detailed tutorial on paste application.
Thanks, Ryan. I'll try to get to this in the next day or so. I still have to inventory my parts to make sure I have everything I need to assemble the board.
I think I've got a piece of 1/8" polycarbonate that will work as a squeegee, assuming there's a factory edge remaining on it. I'll find something, even if it means a trip to the hardware store.
My paste may also be too thick, as James suggested. But I don't have any of the proper flux to thin it with, so may have to proceed with thick paste, unless there's something else that will work for thinning. Isopropyl alcohol comes to mind, since it will volatiilize quickly and should not interfere with the flux action. Or maybe I should just buy a can of paste, since this is definitely the way to paste a board — once I get the kinks out.
I think the big thing is to make sure your paste if fully up to room temperature to get the right viscosity (65-70F is my basement normally). Give a good swirl to mi things up with some sort of stirring rod and you should be fine. The 1/8" polycarb should work well for you. If I didn't say it before your "stencil jig" and tape setup is right on!
Phil Pilgrim (PhiPi) said...
Thanks, Ryan. I'll try to get to this in the next day or so. I still have to inventory my parts to make sure I have everything I need to assemble the board.
I think I've got a piece of 1/8" polycarbonate that will work as a squeegee, assuming there's a factory edge remaining on it. I'll find something, even if it means a trip to the hardware store.
My paste may also be too thick, as James suggested. But I don't have any of the proper flux to thin it with, so may have to proceed with thick paste, unless there's something else that will work for thinning. Isopropyl alcohol comes to mind, since it will volatiilize quickly and should not interfere with the flux action. Or maybe I should just buy a can of paste, since this is definitely the way to paste a board — once I get the kinks out.
-Phil
Phil,
No Isopropyl. It contains water, and will kill the flux. Flux is moisture sensitive (most are anyway). Denatured maybe, but I'm not sure I would try it.
If you buy paste, get it in a "jar". Syringe paste is thin for "dispensing". You may still need flux to thin any paste you buy in a "Jar". Paste is typically a thickness for an automatic stencil printer, and needs to be thinned for hand stenciling.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
Gad! Has it been more than a month already? Well, I'm back on task now with fresh solder paste from Zephyrtronics. I used another circuit board as a squeegee this time, went ahead and placed the parts, and reflowed the board in my IR toaster oven. Here are my observations:
1. The large pads still did not paste completely, but they're easy enough to fill in by hand. (I still think breaking up large paste areas into small islands may be the answer.)
2. The stencil cut the paste-and-place time by at least one half.
3. The board came out of reflow with dime-bright solder joints, excellent fillets, and no rework necessary due to insufficient solder or solder bridges. This is a first for me! There were some stray solder balls that needed to be flicked off, and some other stray solder that did not flux well that went away with the isopropyl alcohol and toothbrush.
All in all, this was an overwhelmingly positive experience. A photo of the reflowed board is attached.
I ended up ordering a large metal stencil for my large boards, and interestingly enough, they took the liberty to break up my large pads into four smaller squares, and taper the smt pads toward the center (for easier placement I guess). I have had good luck using a razor blade for a squeegee. I ordered one of those stainless ones from stencils unlimited, and really like it, though.
I think one of the tricks to getting the pads even is to wipe the solder on one way, and wipe it off the other. (Drywall trade trick)
I just finished pasting, placing, and reflowing three more of those boards using the stencil. They used to take about two hours each using the syringe, and it was about all I could stand to do one or two a day. It took about a third of that time this way, and not a bit of rework has been necessary. I've even discovered a way to fill those large pads: add a little extra paste right next to them just ahead of the squeegee trajectory.
I haven't used Ryan's stencil, but I have used similar stencil with my reflow toaster oven and I love the quickness and the little or now rework compared to hand pasting with a needle. Of course I will still hand paste some for really small prototypes, but if I plan to produce more than one, a stencil is the way to go! I will have to try Ryan's stencils out.
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Timothy D. Swieter, E.I. www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT www.tdswieter.com
What a great thread! Phil I am glad your project went well. The whole idea behind the stencils was to allow a diy'er make the transition from breadboard to small production relatively easily and at low cost. I. The early days of the gps logger I would make 10-20 loggers, receive customer input, change design, sell a few more, repeat, etc. You'll find that the more practice you get the faster things will go. As to pad sizing I do my best to resize large pads so that it is as easy as possible to apply the paste. The other consideration with large pads is that paste can actually creep underneath the stenci, this can make areal mess, especially when assembling multiple boards.
Phil Pilgrim (PhiPi) said...
I'm sold on Ryan O'Hara's stencils!
As am I! Ryan supplied the stencils for our MakerBot at Willoughby & Baltic in Cambridge, MA. All of the PCB's came out beautifully thanks to these stencils.
I'm happy with a kapton stencil from Ryan, too, and also with the quick turnaround and simple ordering he offers. I also have a mylar stencil from Pololu. It's result was acceptable too, but under the microscope the mylar shows more in the way of melted beads around the edges of the apertures. A stainless steel "desktop stencil" is the champ for smooth edges, but it costs more than $100. When I moved such a board past prototype for my regular assembler to do, I had to pay for another stencil anyway to fit their frames.
I wonder if it is okay to use the thin stainless steel squeegee on the kapton stencil, any danger of scratching?
Phil, I'd guess that the main problem was the thermal mass and large pads of the phone jack, is that right? How about the ground pin and tabs for the SOT89 package? One would like to make a large thermal plane to carry way heat in operation from the package, but that goes against effective soldering. Pros seem to be able to work with a mix of parts and different thermal masses.
Tracy Allen said...
Phil, I'd guess that the main problem was the thermal mass and large pads of the phone jack, is that right? How about the ground pin and tabs for the SOT89 package?
Yes, those were the two trouble spots for pasting. I've vascillated on reflowing the phone jack, though. Before, I had left it off so it wouldn't be in the way of any rework I had to do on the Propeller pads. Once I determined that no rework was necessary using the stencil, I reflowed one, but my oven was too hot for the plastic, and it blistered. But with a lower temp (425°F), I'm still getting good wetting with the Zephytronics solder, so I reflowed the connector again on the last board with good results.
Selective pasting near the large pads before squeegeeing seems to have cured any pasting issues I was having anyway.
The thermal masses of the SOT89 and phone connector don't seem to be an issue for reflowing. I preheat to to 285°F for 2½ minutes, then raise to reflow temp for 1 minute. As soon the the minute is up, I open the door to cool.
Tracy, thanks for mentioning the Zephyrtronics solder paste. It's giving much better results than I got with the Kester paste and is much cheaper, since it'll all get used before the flux goes bad.
Phil Pilgrim (PhiPi) said...
Thanks, all, for the input!
My main interest in the solder stencils is for short-term prototyping rather than production runs. Frankly, I've just about had it with clogged fine-tipped syringes! I've looked at some of the Chinese knockoffs on eBay. One site comes with several detailed videos regarding mirror alignment, grounding, and watercooling (using a five-gallon bucket!). This all seems a bit half-a**ed and prone to maladjustment, but the price is down around $1600. On the flipside econonomically, middle-of-the-line Epilogs go for about $15K. That buys a LOT of solder stencils from service bureaus and is WAY above my budget. So this is one purchase I may end up putting off for awhile. :-(
-Phil
hello Phil,
Since the discussion is about prototypting and SMT stencils, I just wanted to bring to your attention that Applied Electronics provide both Mylar and Kapton SMT stencils. Starting this coming Thursday (June 25th), we will take order for Kapton too. You can choose either Mylar or Kapton of size 8.5x11 inch (actual size for Kapton is 8.5x12) without any restriction on the area or number of components.
Mylar comes in thickness of 3 and 4 mil.
Kapton comes in thickness of 3 mil only.
Visit the following site for detail http://www.applied-electronics.com
Just in case you hadn't seen this a customer of mine who makes short runs of pcb's for sale has made a really nice review on how to use stencils and an over for rework.
you make great stencil. Purchased mine for assembling propmods from you.
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propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5
Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.
Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
Comments
Almost all proto PCBs come HASL solder-plated, and I assume you have to add flux; but how do you get the parts to stick to the board before you put them in the oven? And is the plating enough solder for reflow?
James,
One thing I've noticed with Kapton is that it's a lint magnet. Another trick I've gotten from auto detailers (but have not yet tried) is that perfume-free clothes dryer (fabric softener) sheets, when used as a wiping cloth, will reduce the static charge. I believe they're also lint-free.
-Phil
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
I was reading a book on soldering techniques. There was a chapter or two on laser soldering. The book had all sorts of math and science in it and I sat down and read some of it, but not enough to soak it all in. I wonder if it is possible to do this with the desktop machines.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com
I agree, some PCB manufacturers do put enough solder on the pads to do just this. But I have seen a lot of boards that would leave the joints "dry". It depends on who does the boards, and what type of solder.
By industry standard, there shouldn't be enough solder on the pads to do this. If you ask why, because solder when thick, will confuse the registration cameras in automatic machines. The machines require a perfectly flat, thin, solder finish (if the fiducials are coated).
This is one reason we are starting to ask customers why type of plating their boards have. If solder, we reduce the stencil apertures a lot more to prevent bridging. Gold or Silver doesn't get the same treatment.
James L
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
James L
Partner/Designer
Lil Brother SMT Assembly Services
I used to include local fiducials in the pastemask layer but don't anymore. I figured they'd be easier to see and more accurate if they weren't pasted. But a recent batch of boards that my fab house panelized included global fiducials for the panel, and they were added to the panelized pastemask layer. I didn't complain, since I thought they might be handy for the assembly house to align the steel pastemask against. But I have no idea what's standard in the biz. People just seem to take what I give them without comment.
-Phil
Phil,
The best method is to keep the solder off. We, who assemble boards, do use whatever is sent, and many do not comment back. We, as a company, try to educate our customers of what is the best method for success.
Most assemblers use vision systems to align boards to the Pick & Place and the stencil printer. Visions systems use contrast to "find" the center of the fiducial. With solder on the pads, the contrast varies from center to edge (rounded surface of the solder), and causes vision system error.
If you ever find a board which is heavily produced (video card, memory chip, etc) that actually has the fiducials on it (many are on the panel edges which have been removed), you will find the fiducial bare, or gold plated. Mass producers know the fiducials must be consistently flat with even contrast on their surface.
It is possible to align a board manually, so even with solder on a fiducial, the boards can be assembled. It just slows the process a little.
James L
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
James L
Partner/Designer
Lil Brother SMT Assembly Services
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Regards, Ryan O'Hara
Check out our $25 SMT Stencils!!!
www.ohararp.com/Stencils.html
I think I've got a piece of 1/8" polycarbonate that will work as a squeegee, assuming there's a factory edge remaining on it. I'll find something, even if it means a trip to the hardware store.
My paste may also be too thick, as James suggested. But I don't have any of the proper flux to thin it with, so may have to proceed with thick paste, unless there's something else that will work for thinning. Isopropyl alcohol comes to mind, since it will volatiilize quickly and should not interfere with the flux action. Or maybe I should just buy a can of paste, since this is definitely the way to paste a board — once I get the kinks out.
-Phil
I think the big thing is to make sure your paste if fully up to room temperature to get the right viscosity (65-70F is my basement normally). Give a good swirl to mi things up with some sort of stirring rod and you should be fine. The 1/8" polycarb should work well for you. If I didn't say it before your "stencil jig" and tape setup is right on!
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Regards, Ryan O'Hara
Check out our $25 SMT Stencils!!!
www.ohararp.com/Stencils.html
Phil,
No Isopropyl. It contains water, and will kill the flux. Flux is moisture sensitive (most are anyway). Denatured maybe, but I'm not sure I would try it.
If you buy paste, get it in a "jar". Syringe paste is thin for "dispensing". You may still need flux to thin any paste you buy in a "Jar". Paste is typically a thickness for an automatic stencil printer, and needs to be thinned for hand stenciling.
James L
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
James L
Partner/Designer
Lil Brother SMT Assembly Services
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
Yes, it does remove it well, but I don't think I would thin solder paste with it.
James L
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
James L
Partner/Designer
Lil Brother SMT Assembly Services
1. The large pads still did not paste completely, but they're easy enough to fill in by hand. (I still think breaking up large paste areas into small islands may be the answer.)
2. The stencil cut the paste-and-place time by at least one half.
3. The board came out of reflow with dime-bright solder joints, excellent fillets, and no rework necessary due to insufficient solder or solder bridges. This is a first for me! There were some stray solder balls that needed to be flicked off, and some other stray solder that did not flux well that went away with the isopropyl alcohol and toothbrush.
All in all, this was an overwhelmingly positive experience. A photo of the reflowed board is attached.
-Phil
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propmod_us are now in stock. propmod_1x1 arrive on 26th. Only $30
Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.
I think one of the tricks to getting the pads even is to wipe the solder on one way, and wipe it off the other. (Drywall trade trick)
I'm sold on Ryan O'Hara's stencils!
-Phil
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Regards, Ryan O'Hara
Check out our $25 SMT Stencils!!!
www.ohararp.com/Stencils.html
As am I! Ryan supplied the stencils for our MakerBot at Willoughby & Baltic in Cambridge, MA. All of the PCB's came out beautifully thanks to these stencils.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
-Paul
I wonder if it is okay to use the thin stainless steel squeegee on the kapton stencil, any danger of scratching?
Phil, I'd guess that the main problem was the thermal mass and large pads of the phone jack, is that right? How about the ground pin and tabs for the SOT89 package? One would like to make a large thermal plane to carry way heat in operation from the package, but that goes against effective soldering. Pros seem to be able to work with a mix of parts and different thermal masses.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com
Selective pasting near the large pads before squeegeeing seems to have cured any pasting issues I was having anyway.
The thermal masses of the SOT89 and phone connector don't seem to be an issue for reflowing. I preheat to to 285°F for 2½ minutes, then raise to reflow temp for 1 minute. As soon the the minute is up, I open the door to cool.
Tracy, thanks for mentioning the Zephyrtronics solder paste. It's giving much better results than I got with the Kester paste and is much cheaper, since it'll all get used before the flux goes bad.
-Phil
Since the discussion is about prototypting and SMT stencils, I just wanted to bring to your attention that Applied Electronics provide both Mylar and Kapton SMT stencils. Starting this coming Thursday (June 25th), we will take order for Kapton too. You can choose either Mylar or Kapton of size 8.5x11 inch (actual size for Kapton is 8.5x12) without any restriction on the area or number of components.
Mylar comes in thickness of 3 and 4 mil.
Kapton comes in thickness of 3 mil only.
Visit the following site for detail
http://www.applied-electronics.com
Regards
Applied Electronics
http://www.circuitsathome.com/production/on-reflow-soldering
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Regards, Ryan O'Hara
Check out our $25 SMT Stencils!!!
www.ohararp.com/Stencils.html
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5
Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.
Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.