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| Parallax Forums > Public Forums > Propeller Chip > New 4.3" touchscreen LCD for Propeller: Breakout Boards Shipping! | Forum Quick Jump
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James Long
Lil Brother SMT Assembly Services
      
Date Joined Aug 2004
Total Posts : 976
| Posted 11/5/2009 5:16 PM (GMT -8) |   | JRetSapDoog said...
Pardon my ignorance, but what is the use of the laser-cut stencil? Does it expedite the soldering of components? I guess that's the obvious implication (though I could be wrong). But if that's the case, I'm wondering why the stencil helps. That's probably obvious, too. Does it keep the solder where it belongs? Also, funcitonally, how is that different from a PCB soldermask? Oh, and if it does facilitate quicker or more accurate soldering, is it pretty heat-resistant? What is the stencil made of?
JR,
The stencil is for surface mount parts. Each part has a pad which will contain solder which will not only connect the part, but also hold the part on the board.
The stencil facilitates putting down solder paste (like tooth paste), on each pad without putting down solder paste all over the board. The stencil only has holes where each part has pads. Stencils are usually only used for surface mount parts, although I have seen some through hole parts use a stencil as well.
A stencil can be made from Mylar, Kapton, or stainless. The prices increases from Mylar to Stainless. There are also electro-formed stencils which are very expensive (built up plating).
The way surface mount works is: put the paste down with the stencil
put all the parts on the board where they go
bake the board, parts and solder paste until the solder flows (to a certain temperature)
let the board cool, but not too fast. Too fast will make the solder joints be less then optimum.
Solder mask is the material on the board to prevent the solder from "running" down a bare copper trace. If you have ever soldered a perf board you will notice solder will tend to flow every where there is bare copper. The solder mask is there to prevent this.
If you need more information, PM me, and I can send you some links for reading.
James L
James L
Partner/Designer
Lil Brother SMT Assembly Services
Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos! | | Back to Top | | |
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JRetSapDoog
Registered Member
Date Joined Jul 2009
Total Posts : 62
| Posted 11/5/2009 6:53 PM (GMT -8) | | | James, thanks for the useful info (and quick response). Okay, so no heat gets near the stencil...as it's only used to apply paste (I'm assuming that you remove the stencil prior to placing the board in the oven). I was (apparently wrongly) assuming he'd use an iron (figured he was +10X faster than me, lol). I thought folks would only bake boards if they had those "nasty" BGA chips (with hundreds of solder balls in the area of a fingernail), or possibly the Prop QFN package, as opposed to the much more "user-friendly" QFP. As for me, I've hand-soldered some SMD devices, mostly discrete components, but I haven't tackled the Prop QFP yet, which people here say is not too difficult, particularly with a little solder braid/wick to touch-up. Hope they're right. The Prop II will have even finer pitch, so maybe I should start practicing on the Prop I. | | Back to Top | | |
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mctrivia
Registered Member
Date Joined Jan 2009
Total Posts : 2535
| Posted 11/5/2009 7:00 PM (GMT -8) | | | | |
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James Long
Lil Brother SMT Assembly Services
Date Joined Aug 2004
Total Posts : 976
| Posted 11/5/2009 7:29 PM (GMT -8) | | JRetSapDoog said...
James, thanks for the useful info (and quick response). Okay, so no heat gets near the stencil...as it's only used to apply paste (I'm assuming that you remove the stencil prior to placing the board in the oven). I was (apparently wrongly) assuming he'd use an iron (figured he was +10X faster than me, lol). I thought folks would only bake boards if they had those "nasty" BGA chips (with hundreds of solder balls in the area of a fingernail), or possibly the Prop QFN package, as opposed to the much more "user-friendly" QFP. As for me, I've hand-soldered some SMD devices, mostly discrete components, but I haven't tackled the Prop QFP yet, which people here say is not too difficult, particularly with a little solder braid/wick to touch-up. Hope they're right. The Prop II will have even finer pitch, so maybe I should start practicing on the Prop I.
JR,
You are correct in the assumption that the stencil is removed before baking. It is just for the application of solder paste.
If you want a hint about soldering any fine pitch (QFP's).......tack down two corners. Flux the pins, with a angled tip, solder the board on edge. Take the iron and solder from top to bottom dragging it along the pins. Usually, there will be no bridges, but if there are, it's usually the last two (bottom pair). Once you start doing this method, you will find you can solder a DIP the same way (on the bottom of course) and feed solder to the iron while doing it (surface mount parts do not require much solder.....so just the solder ball on the tip will be enough). Your through hole soldering will get much faster.
At times we rework a lot of parts, and this is the method we use. You can search the internet for vertical drag soldering. It works....and it pretty easy. I do recommend getting a Pana-vise holder which will hold the board vertical. If you don't, you will wish you had.
When drag soldering, flux is your friend. Get a no-clean variety, and low solids if possible. If doing lead-free, flux is a must. Lead-free solder will look like #$!#$! if flux is not used. It will also function the same way.
If you ever do any surface mount with the "skillet" method or the "toaster oven" method, you will only pick up your soldering iron for through hole parts, or rework. Baking will spoil you quick. If you get down to 0402 parts, you may go crazy. It is like playing with glitter, with tweezers. We try to keep all of our parts around 0603 or bigger.
0402's are so small, we can not tell when our Pick & Place is putting them down. We have to stop the machine and get our face close to the board to make sure. The machine is intelligent enough to know if it is picking up parts, but things do get out of adjustment. We like to insure we do not have to place those parts by hand.
James L
James L
Partner/Designer
Lil Brother SMT Assembly Services
Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos!Post Edited (James Long) : 11/6/2009 3:35:54 AM GMT | | Back to Top | | |
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JRetSapDoog
Registered Member
Date Joined Jul 2009
Total Posts : 62
| Posted 11/6/2009 8:54 AM (GMT -8) | | Thanks again, James. Useful information to know. A while back, I watched a couple videos online demonstrating a technique similar to your drag-soldering method.
Right after I sent my last message, I thought, "Hmm...maybe the stencil does stay" (since I really have no idea). But you confirmed that it is removed before heating/baking. I just wonder if it is removed before or after placing the parts (if placing the parts by hand). In either case, guess one has to be a bit careful on removing it so as not to smear the paste (or dislodge parts).
I must say, whatever assembly and soldering techniques Ray is using seem to be working out quite well (whether out-sourced or not). I have his PSM board and the soldering seems quite professional. Based on some comments he made, it sounds like he got his boards through ExprssPCB (as they are of the 2.5"x3.8" form-factor that is available at a good price). But it didn't really occur to me that he would have been able to do such quality assembly (the soldering) at home. And, for all I know, he might not have, going through someone like you instead. But, for example, using a stencil and the baking process and some experience (as you've described), I can see how one could get quality results at home in a reasonable amount of time per board. Of course, it's probably also a "labor-of-love," but such techniques would help. On the other hand, there are quite a few passive devices and what not on Ray's PSM board, so I can see how your pick-and-place 'bot would come in "handy" (I just ordered 2 of them, lol). But his breakout board is more straightforward (but useful, of course), so it would lend itself better to "home-assembly" techniques.
Again, thanks for the useful information and soldering tips (I mean pointers...eh...advice, not tips for a soldering iron). And I'll keep your company's services in mind should I ever get in over my head (if I'm not already). Post Edited (JRetSapDoog) : 11/6/2009 5:01:49 PM GMT | | Back to Top | | |
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James Long
Lil Brother SMT Assembly Services
Date Joined Aug 2004
Total Posts : 976
| Posted 11/6/2009 9:10 AM (GMT -8) | | JRetSapDoog said...
Thanks again, James. Useful information to know. A while back, I watched a couple videos online demonstrating a technique similar to your drag-soldering method.
Right after I sent my last message, I thought, "Hmm...maybe the stencil does stay" (since I really have no idea). But you confirmed that it is removed before heating/baking. I just wonder if it is removed before or after placing the parts (if placing the parts by hand). In either case, guess one has to be a bit careful on removing it so as not to smear the paste (or dislodge parts).
I must say, whatever assembly and soldering techniques Ray is using seem to be working out quite well (whether out-sourced or not). I have his PSM board and the soldering seems quite professional. Based on some comments he made, it sounds like he got his boards through ExprssPCB (as they are of the 2.5"x3.8" form-factor that is available at a good price). But it didn't really occur to me that he would have been able to do such quality assembly (the soldering) at home. And, for all I know, he might not have, going through someone like you instead. But, for example, using a stencil and the baking process and some experience (as you've described), I can see how one could get quality results at home in a reasonable amount of time per board. Of course, it's probably also a "labor-of-love," but such techniques would help. On the other hand, there are quite a few passive devices and what not on Ray's PSM board, so I can see how your pick-and-place 'bot would come in "handy" (I just ordered 2 of them, lol). But his breakout board is more straightforward (but useful, of course), so it would lend itself better to "home-assembly" techniques.
Again, thanks for the useful information and soldering tips (I mean pointers...eh...advice, not tips for a soldering iron). And I'll keep your company's services in mind should I ever get in over my head (if I'm not already).
The removal of the stencil can be somewhat critical, but not as bad as most think. It is removed before the components are put down. If using leaded solder most home baked boards do have a nice appearance. They are professional quality. The professionals use the same method. They just have fancier equipment to do the same thing.
There are many people putting out high quality items using the home baking method. Their methods may not be perfect, but they get close to perfect results. I've even seen boards reflowed with a clothes iron. Not a method I would recommend, but I know it can be done.
We haven't done any work for Ray. I believe he is doing it himself. It is not uncommon for someone to produce small quantities of quality items. We are the next step in quantity, when a person doesn't want to do 100 boards by hand.
If you want to read more....look for SparkFun and find the "skillet" reflow method on their site. It gives a detailed step by step procedure of how you can do this at home.
Ray, sorry for hijacking your thread. I think your touch screens are going to be a huge success.
James L
James L
Partner/Designer
Lil Brother SMT Assembly Services
Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos! | | Back to Top | | |
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JRetSapDoog
Registered Member
Date Joined Jul 2009
Total Posts : 62
| Posted 11/6/2009 9:31 AM (GMT -8) | | | You guys are a wealth of information; thanks James and McTrivia. I'll check out the vid. Ray is too busy baking boards right now during his lunch hour to respond. | | Back to Top | | |
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Rayman
Registered Member
Date Joined Jul 2007
Total Posts : 2408
| Posted 11/6/2009 3:01 PM (GMT -8) | | | | |
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mctrivia
Registered Member
Date Joined Jan 2009
Total Posts : 2535
| Posted 11/7/2009 11:17 AM (GMT -8) | | | | |
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Rayman
Registered Member
Date Joined Jul 2007
Total Posts : 2408
| Posted 11/7/2009 11:30 AM (GMT -8) | | | | |
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mctrivia
Registered Member
Date Joined Jan 2009
Total Posts : 2535
| Posted 11/7/2009 12:10 PM (GMT -8) | | | | |
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Forrest
Registered Member
Date Joined Aug 2004
Total Posts : 1222
| Posted 11/7/2009 3:05 PM (GMT -8) | | Rayman,
If your boards are vscored on both sides (which is the industry standard practice), then you should be able to simply place the scored edge on the edge of table and snap them apart with a swift hand.
Forrest | | Back to Top | | |
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Rayman
Registered Member
Date Joined Jul 2007
Total Posts : 2408
| Posted 11/7/2009 4:12 PM (GMT -8) | | | | |
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mctrivia
Registered Member
Date Joined Jan 2009
Total Posts : 2535
| Posted 11/7/2009 5:06 PM (GMT -8) | | | | |
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Rayman
Registered Member
Date Joined Jul 2007
Total Posts : 2408
| Posted 11/8/2009 4:35 AM (GMT -8) | | | | |
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