EEVblog Electronics Community Forum
Electronics => Manufacturing & Assembly => Topic started by: peter-h on June 16, 2021, 11:38:03 am
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I need to assemble a panel about 15x20cm. Not often, maybe 10 a year. But it wants to be something which is not totally awful.
I tend to use JLCPCB for the stencils, which last time came in at some huge size (roughly A3) and I had to cut them down.
I see loads of these things for sale, at all different prices. For example Olimex in Germany sell a stencil holder for €950:
https://www.olimex.com/Products/Tools/StencilPrinters/ (https://www.olimex.com/Products/Tools/StencilPrinters/)
and at that price it ought to be gold plated! But their squeeges are reasonably priced. Olimex don't sell to the UK under €200...
Then I see some on Ebay where even the most expensive are 1/5 of the Olimex price, but obviously these will be chinese and some/most will be junk; the £80 ones are visibly crap
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=solder+paste+printer&_sacat=0&LH_TitleDesc=0&_odkw=stencil+holder&_osacat=0 (https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=solder+paste+printer&_sacat=0&LH_TitleDesc=0&_odkw=stencil+holder&_osacat=0)
Also all the Ebay ones I can see need framed stencils.
My boards are double sided so I need a means of supporting them underneath while printing the topside.
I use a hot air gun to reflow the solder.
Most of the time (a day or so) is spent placing the components.
Any suggestions much appreciated.
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I use PCBway, and their stencils also are pretty big. Way bigger than the board. But, I had a plate with notched bars for the board to sit in, and was able to rig a hinge to it and clamp the stencil frame to the the hinge with C clamps.
Before that, I made my own stencils out of 0.003" brass shim stock, and those were made to be just about 50 mm bigger than the board. I used masking tape as the hinge. So, an unframed stencil can work fine, expecially with less than cutting-edge lead pitch on components.
I'm not sure the commercial stencil holders are any better than the thing I made up myself.
As for a squeegee, I use a piece of 0.025" thick brass shim material. It is visible to the left in the second picture. I also have a shower tile squeegee from Ikea that works, but is harder to clean.
Jon
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For what it's worth, JLCPCB lets you change the size of the stencil. Not only that, if you reduce the size of the stencil by a relatively small amount, it drops the shipping cost quite a bit.
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I'm not sure the commercial stencil holders are any better than the thing I made up myself.
Yeah I don't think it's any worse (and possibly better) than our standard Chinese stencil holder. We have it purely for prototyping and backup if our automatic printer were to fail.
For what it's worth, JLCPCB lets you change the size of the stencil. Not only that, if you reduce the size of the stencil by a relatively small amount, it drops the shipping cost quite a bit.
Indeed, there's really no reason not to order a stencil with your prototypes these days when you can reduce the stencil size down so it has no impact on freight cost.
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I would recommend using a framed stencil. It provides stability and flatness on the stencil. I don't use any stencil printer and only lay the stencil on top of the PCB. Have been doing this for more than 40K of PCB down to 0.4mm pitch. Only during 1 off prototype I would use the smaller custom size without frame JLCPCB stencil. Before that, even for prototype I would used framed ones but the amount of waste I created prompted me to reserve them for production run only. At times, I would have 50-60 framed stencil that is not being used anymore. For low volume, even those cheapest stencil printer in the links you posted works fine. It all depends on your technique to apply the paste and a good USD5 squeegee (https://www.aliexpress.com/item/32971053685.html?spm=a2g0o.productlist.0.0.326d273aPbIrdE&algo_pvid=9d7545d9-c49b-4814-80a7-07f3c70b82cb&algo_exp_id=9d7545d9-c49b-4814-80a7-07f3c70b82cb-1).
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The frustrating thing is that every "cheap" printer I can find is for framed stencils e.g.
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20210617022933&SearchText=solder+paste+stencil+printer+ (https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20210617022933&SearchText=solder+paste+stencil+printer+)
Even the most expensive there, say USD 600, are for framed stencils only.
The cheapest frameless printer I can find is that €950 SD-240 one posted above (which is sold by various firms although Olimex seem to be the cheapest).
For production, stencils are always framed, but then I don't use JLCPCB for production of anything; the company has basically no "communication capability" (ok; that's a general issue with China; one ends up using the firms which have somebody who speaks English) so you never quite know what will come in the post. Production stencils we get made from panel gerber by the assembly outfit, down the road from us.
I missed this previous thread - same sort of debate :)
https://www.eevblog.com/forum/manufacture/stencil-printers-what-to-buy/25/ (https://www.eevblog.com/forum/manufacture/stencil-printers-what-to-buy/25/)
There is one frameless printer from china:
https://www.aliexpress.com/i/4000124287041.html (https://www.aliexpress.com/i/4000124287041.html)
but reportedly the company won't ship to the UK.
Now looking for a reflow oven. Never knew how cheap they are! It looks like the T962 is what everybody is selling, and Aliexpress shows them at a wide range of prices.
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If you're doing 10 per year only (same advice if you were doing 10 per week) - just use an unframed stencil, piece of plywood, some 2" parcel tape and some old PCB's.
Takes less than 5 minutes to set-up. Hell, even if you don't have the plywood - you can do it on a desk.
I'm tempted to do a guerilla video of it - perhaps someone has done one already on YT.
As for the reflow - buy a (toaster) oven, if you've got a K type thermometer then great, else just use a torch/flashlight and watch the board - most ovens have are slow enough to work well. Just wait for the solder paste to change state and add 60 seconds, then switch-off and crack the door so it doesn't cool at >4C per second.
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I have done a few jobs with just the stencil, as you suggest, and with a "fixture" and some tape, it works ok.
But for 10/week, not so sure. Still, the hand assembly of the components does dominate the total time, but it is hard to get pasting consistency if the stencil is not properly stretched.
And reflow with a hot air gun (I have a WEP 858D which is very good) is ok for discretes but much less good for big chips on which you really need to heat up the whole chip at the same time to make it "sit down".
I thought the temp profile is important on the way down too; +300C or whatever for 5 mins won't do some bits much good. Especially some connectors.
Somebody is selling an upgrade for the T962: https://www.ebay.co.uk/itm/192675772419 (https://www.ebay.co.uk/itm/192675772419)
The oven itself is cheap: https://www.ebay.co.uk/itm/123687959494 (https://www.ebay.co.uk/itm/123687959494)
Just bought these two so will report :)
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300oC :scared:
Typical solder paste we use melts around 217oC - we don't take it much beyond 240-250oC normally.
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I am sure you know the T-962 has the smaller tray. It is what I use. I also updated with the United Engineering free firmware and added the Maxim sensor in parasitic mode. Very easy. For calibration and adjustment, I used a couple of small TC's inserted through the bottom (tray closed), set close to the oven TC's, and a portable meter.
BTW, I like the tool plate you used. Mine is smaller and was only about $35 from a US small shop (ebay). The hold-downs were machined at home. My real mill is in storage, so I had to make do with hat washers rather than the nice rabbets. I just use tape on the upper hold-down.
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Can anyone offer a comparison between these two:
https://www.olimex.com/Products/Tools/StencilPrinters/SD-240-Stencil-Printer/ (https://www.olimex.com/Products/Tools/StencilPrinters/SD-240-Stencil-Printer/)
https://www.ams-electronics.co.uk/shop/capital-equipment/pick-place/surface-mount-placement/neoden-fp2636-manual-stencil-printer/ (https://www.ams-electronics.co.uk/shop/capital-equipment/pick-place/surface-mount-placement/neoden-fp2636-manual-stencil-printer/)
The FP2636 is much bigger, but apart from that...
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I've ordered the SD240 (from Olimex; the UK disti wanted a load more £££) and will report on how it works.
Got the T962 reflow oven also. Needs some mods ;)
https://www.eevblog.com/forum/manufacture/t962-reflow-oven-233972/50/ (https://www.eevblog.com/forum/manufacture/t962-reflow-oven-233972/50/)
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Peter,
I have the SD-360, the same as yours, just larger and with parallel lift of the stencil.
https://spide-smt.nl/portfolio-item/sd360-u/
The build quality, adjustment possibilities etc are very nice.
I use (frameless) stencils from JLC in it
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Peter,
I have the SD-360, the same as yours, just larger and with parallel lift of the stencil.
https://spide-smt.nl/portfolio-item/sd360-u/
The build quality, adjustment possibilities etc are very nice.
I use (frameless) stencils from JLC in it
That looks great! Do you find it easy to tension the stencil, and the magnetic pcb mounts work well? I can't see in the manual where it specifies the tooling hole size for the pcb holders - do they come with a few different sizes or do they have one that can position a board by the corners?
EDIT : From photos it looks like the magnetic PCB holders simply locate the PCB by the board edge - no tooling holes required. Nice. Plus you get a couple of support ones to position under large boards to limit deflection when applying paste.
Neoden vs Spide - Spide ones look more flexible with the PCB mounting. Currently I'm using a block of MDF, a number of pieces of blank PCB boards taped down to hold the actual board in position, and a stencil taped at the top edge. Works, but a parallel lift stencil printer would likely get better results especially on stencil removal.
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Peter,
I have the SD-360, the same as yours, just larger and with parallel lift of the stencil.
https://spide-smt.nl/portfolio-item/sd360-u/
The build quality, adjustment possibilities etc are very nice.
I use (frameless) stencils from JLC in it
That looks great! Do you find it easy to tension the stencil, and the magnetic pcb mounts work well? I can't see in the manual where it specifies the tooling hole size for the pcb holders - do they come with a few different sizes or do they have one that can position a board by the corners?
EDIT : From photos it looks like the magnetic PCB holders simply locate the PCB by the board edge - no tooling holes required. Nice. Plus you get a couple of support ones to position under large boards to limit deflection when applying paste.
Neoden vs Spide - Spide ones look more flexible with the PCB mounting. Currently I'm using a block of MDF, a number of pieces of blank PCB boards taped down to hold the actual board in position, and a stencil taped at the top edge. Works, but a parallel lift stencil printer would likely get better results especially on stencil removal.
Yes, the tensioning and adjustment (X,Y) of the stencil is very easy!
And you are correct, the magnetic bases sits on the edge of the board and they are very "magnetic", they will NOT move unless you apply a LOT of force on them!
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I think our company's stencil printer may match your demands.This is the link:https://youtu.be/4fAhuh5dBnc:How to use Tronstol TP3040.
We use positioning beads and positioning posts to fix the PCB board, which can meet your double-sided board needs. Its fixing method is very simple.
We also need framed stencils.
And you cost one day to place the components,why don't think to buy one PNP(Tronstol 3V) and mini-reflow oven(Tronstol MR30) to save your time.
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I found this by coincidence and I thought I'd comment since I have the Neoden stencil printer mentioned above. All in all I'm quite happy with it and it works reliably and accurately. My only criticism is that the bearings are rubbish (it has linear bearings on the right and left side to make the front stencil clamp glide back and forth on guide rails while changing the stencil. These bearings failed pretty much after first use so the sliding clamp tends to get stuck on the rails. It doesn't impact the operation much, it just makes the product feel cheap. I would still recommend it any time.
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The SD240 works great. Well made and accurate.
Quite fiddly to set up the PCB locators but I can't see any good way to do that.
I use stencils from JLC and cut them down to size to fit the printer.
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I will receive my Neoden frameless stencil printer next week. Curious to see how well it works.
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Here's a pic of my stencil holding rig : http://pico-systems.com/images/cardholder.jpg (http://pico-systems.com/images/cardholder.jpg)
and here it is with a board sitting on the ledge : http://pico-systems.com/images/cardholderwcard.jpg (http://pico-systems.com/images/cardholderwcard.jpg)
In the back right of these images you can see my squeegee which is a piece of .025" brass shim stock material.
And, here it is with an unframed stencil : http://pico-systems.com/images/cardholderwstencil.jpg (http://pico-systems.com/images/cardholderwstencil.jpg)
The stencil is held by a piece of masking tape and it works as a hinge.
I now use framed stencils from PCBway, they are amazingly cheap, and I added a hinged plate at the rear of the base of this fixture to allow the stencil frame to be clamped to that plate. For fine-pitch alignment, I use a magnifier to look at the pads on the board and align the stencil. For ordinary SOIC and 0805 parts the naked eye is good enough. I don't find a need for center support of boards less than 250mm wide.
Jon
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Here's a pic of my stencil holding rig : http://pico-
(http://pico-systems.com/images/cardholder.jpg)
Hey Jon, That is similar to what I made. Worked great with a SS stencil for my first real use, after a few trial runs. I used Kapton tape to hold the stencil at the top. Lifter it straight up. My real mill was in storage, so I bought the tool plate and made the rest with a Harbor Freight piece of junk. The MCU footprint is a TQFP.
John
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We started to offer frame for perforated stencils, which fits 3040 printers:
https://www.tronstolsmt.eu/products/sf2838-stencil-frame-for-4-sided-perforated-stencils-280x380-mm (https://www.tronstolsmt.eu/products/sf2838-stencil-frame-for-4-sided-perforated-stencils-280x380-mm)
Saves on space and reduces the stencil + shipping cost. Tensioning is much better and stencil doesn't bend on sides like in 2 sided printers. Custom sizes on request.
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I have the Neoden frameless stencil printer which I purchased under a year ago from AMS in the UK. I'm looking to sell it (upgrading to a full line soon) so if you're interested feel free to PM me. It works great with frameless stencils.
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We started to offer frame for perforated stencils, which fits 3040 printers:
https://www.tronstolsmt.eu/products/sf2636-stencil-frame-for-4-sided-perforated-stencils-260x360-mm (https://www.tronstolsmt.eu/products/sf2636-stencil-frame-for-4-sided-perforated-stencils-260x360-mm)
Saves on space and reduces the stencil + shipping cost. Tensioning is much better and stencil doesn't bend on sides like in 2 sided printers. Custom sizes on request.
I think I can see myself with one of these stencil holders in the future, just what the Doctor ordered. Framed stencils make the shipping reach stupid prices and the white glue they use around the edges starts to crack and disintegrate after a year or so and they take up space.
Can you please add the dimensions to the product listing so I can see what the overall size for the 260x360 holder is.
It looks like I have the same(similar) printer that you stock, so I guess it will work with mine, but the dimensions are good to be sure.
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Not to advertise, but a little known piece of information is that Neoden also makes a pneumatic tensioning frame.
Price $765 + $101 shipp
https://www.neodensmt.com/other-products/smt-stencil-frame.html (https://www.neodensmt.com/other-products/smt-stencil-frame.html)
The photo on their website (when you can find it) doesn't match anymore.
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LPKF has a patent in Europe for this pneumatic frame, they are not allowed to sell it here as it's direct copy(ZelFlex Z4P).
If somebody still buys it, it's very hard to repair it, when it fails(and rubber tube inside will fail after a few years), you need to have the right tools to make it airtight(rings, bending tool and handpress), you need to have the right softness of air tube, etc.
Mechanical frame will hardly fail.
Roughly the frame is 300x400 mm in dimensions, it will fit all the printers for framed stencils, if they are open on sides. I'll update the listing with more technical details.
Currently we have a promotion for a free stencil, if you buy it.
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There are 4-5 commercial stencil frame systems out there. By far the most common is the pneumatic VectorGuard* system from DEK/ASM, its slightly more expensive to implement as the stencils have a light frame on them to keep them safe & semi rigid for storage & washing. However once you stray outside of your JLC type stencil suppliers, pretty much anyone will support this format. The others such as LKPF are less common and some have restrictive licensing which affects their adoption. Another mechanical system is the Tecan Genesis, there's a second hand one here https://www.shawline.co.uk/product.php?id_product=196 (https://www.shawline.co.uk/product.php?id_product=196) quite a few people will implement that for you but Tecan is the obvious choice, tensioning hole/size location is quite critical as it tensions with two 90 degree levers, very quick, very effective but fairly heavy. We go though quite a few stencils and have both these systems (different sizes) the frames are fairly expensive to buy but in both cases we paid nothing in exchange for amortising the cost over the forthcoming stencils. They are worth having if you use a lot of stencils tho' each stencil hangs in a carboard sleeve about 6-8mm thick so there's a distinct space saving.
*There are also compatible variants including a rather complex looking mechanical version.