Stencil printer - Page 1
Forum section: electronics / projects

author: davorin
author_rank: Unknown
timestamp: October 03, 2014, 11:17:35 pm
content: Evenin' (o;As my eyesight gets worse and worse and components smaller and smaller and are mostly available in non-selfsolderable packages..the only way now seems to be going with SMT stencils and either do reflow or vapor phase soldering...But when I searched for stencil printers...I only find commercial products....nowhere any construction plans to be found for building an own one....Has anyone came across how to build a simple and still accurate stencil printer which can handle fine pitch down to 0.4mm?I have enough metal lying around and two CNC machines for building (o;

author: sleemanj
author_rank: Super Contributor
timestamp: October 03, 2014, 11:38:35 pm
content: Do you mean a stencil cutter, or an actual stencil printer (device to align a stencil over the board and spread the paste)?Regarding cutting, people obtain very good results from cutting stencils from transpencies using the "Gerber2Graphtec" scripts and Silhouette Cameo or Portrait craft cutters, down to about 0.5mm pitch, 0201 discrete components...https://github.com/pmonta/gerber2graphtechttp://dangerousprototypes.com/forum/viewtopic.php?f=68&t=5341If it's an "printer" you want, that's a different matter.

author: tggzzz
author_rank: Super Contributor
timestamp: October 03, 2014, 11:45:44 pm
content: Stencils are only beneficial if you are making many copies of an individual board. It takes significant practice to use them well. If you are making many boards, consider getting them manufactured externally.If you are only making one board, thenget the board made with a solder maskuse a magnifying visor with a lens mounted on a headband (with your glasses if necessary)place the solder paste with a toothpick or jewellers screwdriverWhen reflowing, e.g. in a saucepan, the paste will retract away from the solder mask.There are many videos on youtube showing this.

author: zapta
author_rank: Super Contributor
timestamp: October 04, 2014, 12:22:39 am
content: Quote from: tggzzz on October 03, 2014, 11:45:44 pmI tried it with 0.5mm pitch and it was very difficult.Anybody has any experience with those dispensers? They are supposed to delivered a measured amount and have a negative pressure at the end to stop dripping. Currently I am using stencils but this may be a better approach for prototyping.

author: Spikee
author_rank: Frequent Contributor
timestamp: October 04, 2014, 12:52:50 am
content: Quote from: sleemanj on October 03, 2014, 11:38:35 pmI do this for my own projects. But i also offer my stencil service on ebay. You need to make quite a few stencils to get to the break even point. It might be more economically viable to get them made for you. Heck i offer a4 size stencils for 10$ with fast shipping, that is not a bad deal at all.They are really easy to use and save you a lot of time versus hand soldering. Even sparkfun uses a vinyl cutter to make stencils for all their prototype boards.

author: zapta
author_rank: Super Contributor
timestamp: October 04, 2014, 05:54:04 am
content: Quote from: Spikee on October 04, 2014, 12:52:50 amPlastic or metal? Do you have a web site?I use oshstencils.com for plastic but they are not great for 0.5mm pitch. Metal stencils from elecrow give more accurate results but are more expensive (~$20 + shipping).

author: hagster
author_rank: Frequent Contributor
timestamp: October 04, 2014, 06:15:19 am
content: Have a look at this video from eurocircuits about their ec stencil fix system. You can do something similar yourself very cheaply.the key is getting stencils and pcbs with registration holes.

author: tggzzz
author_rank: Super Contributor
timestamp: October 04, 2014, 08:41:11 am
content: Quote from: zapta on October 04, 2014, 12:22:39 amHave a look atand the follow-onto see how lax you can be even without a solder mask. I wasvery pleasantlysurprised.There are other youtube vids showing "excess" solder paste retreating to the lands.

author: Spikee
author_rank: Frequent Contributor
timestamp: October 04, 2014, 10:07:44 am
content: They are transparant plastic (3m materiaal), i use thema all the time for 0.5mm pitch parts (qfn, msop) and alsof for bga.The link is in my forum profileren (ebay).

author: davorin
author_rank: Unknown
timestamp: October 04, 2014, 01:55:15 pm
content: Actually I'm talking about a device where you can adjust the PCB and stencil on top and paste the solder paste onto it...Many PCB companies like Eurocircuits are offering laser stencils for a few bucks more...and as I would like to do PCBs containing BGA chips like FPGAs and power supply ICs in FQN packages just put some flux onto the pads won't do good from my experience...thh smaller chips just float away in the Galden LS230 steam (o;I have a small Pizza oven though...but I can alrey here my girlfriend complaining about the smell (o;

author: David_AVD
author_rank: Super Contributor
timestamp: October 04, 2014, 09:26:47 pm
content: Quote from: zapta on October 04, 2014, 12:22:39 amWe use one of those at work. It works quite well.

author: mjkuwp
author_rank: Unknown
timestamp: October 04, 2014, 10:30:15 pm
content: in the USA.I use ohararp,com for kapton stencils made by laser. They are good for 0.5mm QFNL. I have made half a dozen now off the same stencil. My opinion is that even if you are making one board a stencil may be the best route if you have really challenging parts.For boards that do not have such a fine pitch I use solder paste from a syringe but the paste from the syringe does not work well for the stencil. I bought syringes loaded with solder designed for that type of dispensing.Solder for stencil: SMD291AX250T3-ND from Digikey (leaded, no-clean flux, paste). Has worked really well.Solder for syringe came from:http://www.zeph.com/zephpaste.htmI can see how a dispensing machine would be nice to use but at that point of having more boards to do or more detail I personally would go for the stencil.I am not claiming to be an expert but my results have been good. In particular I really like the no-clean flux because the boards look really nice directly out of the oven.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 04, 2014, 11:47:14 pm
content: For me, as I have moved to smaller and smaller parts, the days of iron/wire are largely gone. Even though it's possible, I don't bother anymore since there are so many great options out there from super DIY/cheap to over-the-top sophisticated.My daily work includes prototyping and and small batch production with SMD passives down to 0402, but more typically 0603 and 0804. .4mm QFN's present the biggest challenge for me, but I have managed to become friends with those packages after some patient hours of trying.SUPER CHEAP:Manual syringe with TYPE 5 solder. It's more expensive, but the very fine solder powder allows me to use fine needles which is critical. Putting paste down with toothpicks is a waste of time unless the components are huge. If you have a few components, this works. The downside is that its hard to be consistent and your hand will get tired pushing paste through a tiny 22ga needle.PROTO STENCILS:These things can be pretty handy and don't cost much. I have always been dissapointed with Kapton for small pitch devices. The PROTO STENCILS from houses like STENCILS UNLIMITED and SUNSTONE are steel and have the edges bent into a box. They include a whole placement and squeegee kit. I have used these with pseudo success with .5mm but it takes a delicate touch and some practice. Generally not very consistent since they are not stretched and just taped down. Saved my butt on a few projects before I had a real printer.COUPLE 'O BUCKS:I also have a Zephytronics Air Mill solder paste dispenser which is quite awesome. The machine allows consistent deposits without any effort. This setup allows a lot better precision because your muscles are focused on placement while the machine does the hard work of pushing the paste out. Even though it has a timer, I just put it on manual an control the output by "feel". The learning curve was a few hundred components and then I was plowing through proto projects faster than I could order-receive-setup a stencil. I have been successful at using this method to place fine pitch but it is not a free lunch. The pad design is critical for leadless devices and I generally have to do some hand work after re-flow.COUPLE MORE BUCKS:Cheap printers for framed stencils are a big step up - but cheap means cheap. I looked at most of them and they are all marginal pieces of machinery, but still a quantum leap forward compared to the previous options. I got the MANNCORP RT2100. They are not kidding when they say "Entry Level Printer". I am a machinist [and MECH ENGINEER] with a 5-axis CNC shop so I was able to make modifications and PCB holders that were good enough for .4mm pitch. It is no longer a chore to deal with fine pitch, I have done hundreds of PCBs with this setup followed by 100% manual placement of components and NONE failed. If I did not have the resources to modify the machine myself, I would have been looking at the $3k models. The problem with the low-end it that they are hard to get a good alignment and tend to be be jiggly. The problem with the higher-end, is that they get expensive real fast. Starting with a low-end machine and modifying it was a fast way for me to get great results. Not everyone is looking for a CNC project though. Without the mods, I would have thrown the RT2100 off a bridgee.I had been looking at various P&P machines but decided that going in the order of OVEN first, PRINTER, second, and P&P third is a good path. The addition of the stencil printer has been awesome.

author: joshhunsaker
author_rank: Contributor
timestamp: October 05, 2014, 06:49:18 pm
content: Quote from: zapta on October 04, 2014, 12:22:39 amYou can buy a very cheap set of syringes to use to dispense solder paste extremely accurately:http://www.ebay.com/itm/10CC-Syringe-SMT-SMD-PCB-Solder-Paste-Adhesive-Glue-Liquid-Dispenser-EFD-Loctite-/221234842565They have some very small tips for it. Mess-free.

author: tggzzz
author_rank: Super Contributor
timestamp: October 05, 2014, 07:07:54 pm
content: Quote from: joshhunsaker on October 05, 2014, 06:49:18 pmMy very limited experience of hand placing paste through a small (0.5mm) needle is that it was a pain; I preferred the screwdriver/toothpick technique for small prototype boards.The principal problems were that a "high" pressure was required, and the paste continued to flow after pressure was removed. Which wasn't surprising since I didn't have a vacuum to remove the pressure and halt the flow.

author: Marco
author_rank: Super Contributor
timestamp: October 05, 2014, 08:19:36 pm
content: Are those ~100$ electronic dispensers on ebay any good?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 05, 2014, 08:23:16 pm
content: Quote from: tggzzz on October 05, 2014, 07:07:54 pmAs long as all the pressure is released (i.e. vented) quickly , as opposed to just closing a valve to the pressure source, flow will usually stop quickly - I don't recall seeing a suck-back option on any dispensing systems, but not looked very hard

author: tggzzz
author_rank: Super Contributor
timestamp: October 05, 2014, 08:47:16 pm
content: Quote from: mikeselectricstuff on October 05, 2014, 08:23:16 pmWell, I can assure you my finger stopped pushing and the paste continued flowing. The only way to quickly stop the past flowing was to "pull back" on the plunger until the internal pressure in the paste was the same as atmospheric pressure.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 05, 2014, 09:11:49 pm
content: Quote from: tggzzz on October 05, 2014, 08:47:16 pmSorry I thought you were referring to a compressed-air system.Hand dispensing is a pain as you have to use enough force that it's hard to keep the needle in the right place.Foot-pedal operated compressed air is the way to go.

author: tggzzz
author_rank: Super Contributor
timestamp: October 05, 2014, 09:31:01 pm
content: Quote from: mikeselectricstuff on October 05, 2014, 09:11:49 pmRe-reading my comment, it was indeed ambiguous.Actually you can just about let off the finger pressure, relax and position the needle - while the paste slowly erupts. But I found the real aggro is that there was no way stop the eruption when sufficient paste had been deposited. That would continue to be true with any positive-pressure-only mechanism.I have assumed, without checking, that the foot operated machine stop the eruption by sucking the plunger for a short time.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 05, 2014, 10:12:17 pm
content: If your syringe is completely bubble free, the problem of continuous flow is drastically reduced. I purchased the paste in a syringe so it has no bubbles, then transferred it to the actual dispensing syringe with a tapered plastic tip that I cut with a razor blade. Whether being dispensed manually or with my pneumatic machine there is no post-flow to speak of. I almost never use the vacuum option on the pneumatic dispenser and I don't have to pull back the plunger when doing it manually.If you are trying to fill a syringe with a spatula from a jar, it is very unlikely you would not have big bubbles that will make things hard to deal with.

author: zapta
author_rank: Super Contributor
timestamp: October 05, 2014, 10:59:24 pm
content: Are those dispensers stand alone products or do they require external supply of pressure and/or vacuum?

author: rx8pilot
author_rank: Super Contributor
timestamp: October 06, 2014, 12:09:05 am
content: Generally, they all need external compressed air source. The compressed air drives a venturi that created a vacuum as needed. The air requirements are very small. I use a very quiet California Air compressors model that is far more than enough and quiet enough to keep close by. Only $195USD on AmazonI run at 40-60psi with my Zephyrtronics Air-Mill. It was a MAJOR process improvement for me at the time - before I got a stencil printer. It still gets quite a bit of use for small proto boards when it is faster than setting up the printer or when I don't even have a stencil.

author: zapta
author_rank: Super Contributor
timestamp: October 06, 2014, 04:10:50 am
content: Quote from: rx8pilot on October 04, 2014, 11:47:14 pmAre you already using one of those manual P&P with a vacuum pump and pedal? If not, this can be a cheap and very useful increment.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 06, 2014, 04:22:55 am
content: I have an electric vacuum pen and some PCB holders that I machined - no P&P yet. I would like to have something as soon as possible - hand placing 0402 passives and .4mm QFN's is not going to be a fond memory. Decided to skip the manual machines and save up for the real thing.Up to about 225CPH by hand, which is about as good as I will ever be. Even a cheap ($30k) P&P is 10x faster and does not take coffee breaks. It will also allow be to take advantage of panelized PCB's instead of going one at a time.

author: RobK
author_rank: Contributor
timestamp: October 06, 2014, 02:41:19 pm
content: Thought I'd point out that ohararp is now offering stainless steel stencils for a very reasonable price and a great turn time of only 5 days. I've been using the mylar and kapton stencils for years, but with stainless steel now hitting this new price point my days of using the plastic stencils are over I hope.I received my first stainless steel stencil from Ohararp a few weeks ago. If anyone's interested I can post some pictures and a short review

author: zapta
author_rank: Super Contributor
timestamp: October 06, 2014, 03:31:26 pm
content: Quote from: RobK on October 06, 2014, 02:41:19 pmThey seem to be on the high side for hobyiests and do not have 5mils. Last few times I ordered the metal stencils from elecrow together with the PCB's so no additional wait time.http://www.elecrow.com/laser-cut-pcb-stencil-service-without-frame-p-869.htmlhttp://www.elecrow.com/laser-cut-pcb-stencil-service-p-450.html

author: jonroger
author_rank: Regular Contributor
timestamp: April 03, 2019, 01:58:03 pm
content: Seems to me that it would be useful to have a solder paste dispensing syringe with a built-in electrical actuator. Something like the tiny stepper motor/lead screw seen in this ebay item:2-phase 4-wire Micro Mini Stepper Motor 43mm Long Linear Lead Screw Slider ShaftOK, I see it has already been done. But with stepper motors that look overly large/heavy.