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Southern California
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I have a syringe of this:

http://search.digikey.com/scripts/dksearch/dksus.dll?vendor=0&keywords=chip+quik+lead+free+no+clean+35g

I'm having trouble getting a clean stencil mask for a FT232RL chip. Is this the wrong kind of solder paste for a stencil? If so, does anybody have any recommendations?

Thanks,

Chris
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That paste should be OK. Make sure it's room temperature. Temperature is VERY important for solder paste. Your squeegee technique also makes a lot of difference. Don't be afraid to try, clean, try, clean, until you get the hang of it.

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When you stated you can't get a clean stencil for the FTDI IC ... have you tried other footprints?  What's your stencil look like?  Where did you get it made from?  And as RC pointed out, a lot depends on how you're applying it.
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The footprints for the rest of the parts (SOIC, TQFP, 1206, 805, SOT-23) look like they'll work, it's just the fine-pitched FTDI chip I'm having problems with.

The stencil is a Pololu 4 mil Mylar sheet. I think the alignment looks fine with the stencil on top of the board; I will try to take a pic if you think it will help.

The paste was filled Sept 2 2011 and I just opened it today; it's been refrigerated since I got it last fall. It was out for about an hour before I started; I'll leave it out a few more hours. It's slightly runnier than the lead paste I usually use but I thought that was due to the difference in metals.

I will definitely keep practicing; thanks for the tips.


« Last Edit: February 21, 2012, 07:18:06 pm by magagna » Logged

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It looks like it's the paste...I tried with the leaded solder and got good results (attached). Time to find some new lead free paste that hopefully isn't $500 for shipping.

Now to figure out how to place the FTDI chip without smearing the paste...



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sub-ing to thread.

I too am wondering/looking for solder paste to buy to be used with stencils.  (first time/attempt)

Is there a difference/preference on using the lead vs lead-free solder?

What type should be used?  (for both manual application from syringe and jar type for squeegee application?)

is there a place (US) that most people order from?  affordable?  (I really hate paying high shipping fees!)  LOL..

also.. is there any 'LOCAL' places that may have something that is usable at least to do some tests with?
most of the stuff I have seen was for copper/plumbing..etc. (not electronics use)

thanks!  smiley
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Leaded melts at lower temperatures and is overall a little easier to work with, but it's been banned in the EU (RoHS) and some uses in the US. I've been using leaded paste since I started working with SMD components about 6 months ago, but am trying out lead-free for a design I hope to sell.

From what I've read the tube type of paste is runnier than the jar type, because it has to be able to go through the syringe needle. I'm not sure what effect that has on a stencil...hopefully I will be able to tell you soon...but what I can tell you now is that "no clean" is the way to go.

I usually buy through Digi-Key and have been getting their 35g syringes like this:

http://search.digikey.com/us/en/products/SMD291AX10/SMD291AX10-ND/2057271

but yesterday just ordered some of this to try out:

http://www.stencilsunlimited.com/875lf-no-clean-lead-free-solder-paste-250-gram-jar-p-645.html?osCsid=2183dc82191ffa08b3f9d518a00ba66d

I will let you know how it works.

As far as local...I'm not sure where you live but none of the places in southern California (Fry's, Mar-Vac, Radio Shack...) carry paste at all.
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Thanks..

Im located in the upper mid-west, Wisconsin  (cheesehead)  smiley-razz

I havent seen any at a RadioShack or my local mom-n-pop shops either. smiley-cry

(gonna check your links now)
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what type of chip?

I didnt 'shrink/swell' any of my openings for my stencil.. and I did a ATmega 329QTFP chip... (two completes board so far)..

the 0603 components and other components arent anythign special.. IMHO.. but that ATmega had a bit of breath holding as I placed it!  lol

I got an IC sucker/suction pen form dealextreme.. ($4 or so)..

its ok...  but I think you can do just as good with very fine tweezers.

I had a bridge on my first one.. (I thought).. and fixed it with some flux and a bit more solder (wire..not paste)

good luck!...
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I've got some solder paste from ebay, and Ive only used it twice, once for for like 35 0805 leds and 50 0805 resistors, and another with a few soic ics,
I cheaped out and just directly applied the solder paste on the pads with a modified syringe, just a little bit on each and it worked great
I tried two techniques for the soic, one I put paste on each individual pad and the other just a line across all the pads, both methods worked perfect, obviously the line was faster tho
its amazing how well solder paste works and it was much easier than I thought, the way the leds and resistors just pull themself in line not only looks good as a finished product but amazes me everytime as it moves by itself with just the surface tension
How much does it usually cost you guys for the stencils?
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Quote
How much does it usually cost you guys for the stencils?

I've used Pololu and my 3x3" one was about $30 (http://www.pololu.com/catalog/product/446). Wayneft Recently recommended kapton stencils from http://www.ohararp.com/Stencils.html; I will probably try them next time.

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ditto as magagna-

I got my first/only stencil from pololu.com   (was easy and painless)..


but I think my next will be from ohararp.com as well..

I have heard good things.. 

not to mention I heard he will fill up a whole sheet for you (not just one design..but use/fill the whole 8.5x11 sheet)
I was also told he will swell (shrink) the holes for you if needed to make for less solder to get on certain footprints..

(cant beat that!)  smiley  and all for around the same price..

which for me was around $22 bucks with another 8 or so for shipping?
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That's not so bad, how much smd do you usually do on those boards?  Im wondering if its worth it to get a stencil on my next board, probably another 150 or so pads, and individually applying the paste gets a little boring and gets old fast
the board is a mega shield size so the pcb from batchpcb is like 22 $ plus the shipping and handling makes it close to 40$, is the extra 30 worth the cash?
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I guess thats something you'll need to decide for yourself..

the time vs manually application process...vs a stencil....etc..


I used iteadstudio.com for my pc's.. which came to like $10.00 for 10 pcbs'..  (.75 x 1.75 or so in size)

that helped me save on my overall project.

for myself.. I'll never NOT use a stencil.. (unless its like 1 board or something)..

it was SO easy I couldnt believe I had done things correctly.

example of my first board.. using a stencil.. and toaster oven to re-flow:

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I've built maybe two dozen boards now with FT232RL using the ChipQuik lead-free syringe from Digikey and Polulu mylar stencil.  The 0805 and SOIC components come out perfect every time.  But the SSOP chip (FT232) almost always has bridges.  The lack of true flatness of the mylar (it is slightly curled) seems to allow the solder to squeeze laterally under the stencil while being squeegy-ed.  The result is too much paste for the component, hence the bridges.

FWIW, I have found it to be quicker and easier to leave the SSOP chip off the board when reflowing, and then manually solder it.  I put down a healthy layer of RMA flux from a pen-type applicator, and then carefully line up the chip with the footprint on the PCB.  Tack two diagonally opposed corners, then sweep a tinned chisel-style tip across all of the pins.  I've used this procedure on 3 boards now with much better results.

Jim
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