Choosing solder paste and needles

[sentry7]

Hey guys,

I'm shopping for my first tube of solder paste, and there are lots to choose from. Any suggestions? I'm also working with SMD components, and so, I'm going to need a relatively small applicator, are the needles interchangeable?

[georges80]

Since you're in the US, I'd recommend Kester 256 from the vendor below. Decent price and quick delivery and it's GREAT solder paste.

http://www.cmlsupply.com/kester-ep256-lead-solder-paste-63-37-syringe-dispenser/

Comes in a syringe and with several tips that work just fine for 0603 size components.

Store the paste in a SEALED ziplock bag in the fridge to extend the life.

cheers,
george.

[zapta]

I never had luck applying solder paste with a syringe, it doesn't stick to the PCB, so I am using stencils. Do some solder pastes stick better than others?

[georges80]

Kester 256 has "nice" flux (when fresh) and applies nicely to solder pads.

cheers,
george.

[rx8pilot]

I never had luck applying solder paste with a syringe, it doesn't stick to the PCB, so I am using stencils. Do some solder pastes stick better than others?

I had the same issue but continued to work on it. The technique is important as is the paste itself. The Kester is easier to work with IMHO. I have some cheap stuff that can get the job done, but harder to deal with. The savings on the cheap stuff is not worth the hassles to me.

For me, it was very much worth getting the super fine Type 5 (I think that is right) to be able to push the smaller needles. A big needle can only make big blobs, where a small needle can make small or large. The pressure needed for the smaller needles can be considerable though eventually leading me to buy a pneumatic dispensing system which makes a WORLD of difference when using solder paste. I have and love my stencil printer, but when going through 2-3 rapid revisions of a PCB having a  manual paste dispenser saves money and time overall. I can build the PCB in sections, do re-work, and don't have to order and wait for a stencil to arrive that may get used one time.

So far, I have been able to get away with doing .4mm QFN's and up. 0402 is normal, QFP's, etc. The QFN's generally have a couple of bridges, but those are easily pulled up with a soldering iron.

Short needles are easier to push paste through. Bent needles make it easier to apply under a microscope (highly recommended to use microscope). The tapered plastic needles can get clogged easier, guessing that it packs the balls at the tip. The metal tips are much thinner and generally easier to work with.

[plazma]

I use a very thin and a quite short needle on my paste syringe. The needle have been lubricated with a special lubricant. I have to check the brand and code at work.
Without the lubricant it would be impossible to use such a thin needle. Without such a thin needle it would be very hard to manually apply paste to small bga pads.

With a pneumatic dispenser and the lubricated small needle it's surprisingly fast to add paste to a 100+ pad bga footprint.

[rx8pilot]

look forward to hearing more about the needle....is it the teflon coated type?

[Psi]

I never had luck applying solder paste with a syringe, it doesn't stick to the PCB, so I am using stencils. Do some solder pastes stick better than others?

The difference i found between using ChipQuic paste vs Loctite paste was like night and day.

The Chipquik stuff was awful. It didn't stick to the pads much and keep oozing out of the needle after i let go the syringe.

The loctite stuff i bought (its made by multicore, part 583489) was perfect. It stuck to the pads every time.
I could go around the board putting daps of paste anywhere i wanted. It also didn't ooze out.


I think the difference is to do with the size of the solder balls and the percentage of flux vs balls.
For hand work you want smaller solder balls and more flux. This makes it easy to flow throw the needle and sticky so you can put it where you want.

[mikeselectricstuff]

There are quite a few flavours of paste. The main thing is to use a paste designed for dispensing, not stencilling - the former is more runny and sticky.

Another important thing is temperature - if it's too cold, it won't flow and it won't stick - trying to use it fresh from the fridge is hopeless.

Old paste can sometimes be revived by adding some liquid flux and mixing thoroughly.

I was told by one manufacturer that shelf life is as much to do with moisture absorbtion as temperature, so keeping it sealed, maybe with silica gel, is a good idea. 
I've found EFD SolderPlus paste has a very long shelf-life (many years) , but IME is hard to buy in small qtys.

[Bud]

I never had luck applying solder paste with a syringe, it doesn't stick to the PCB, so I am using stencils. Do some solder pastes stick better than others?

I have been using Kester 256 for years, hundreds of boards done, good no-clean paste, no issues with non-sticking in about 1 year from purchase date, and that is when I finish the last year supply and buy a new one.

[zapta]

I never had luck applying solder paste with a syringe, it doesn't stick to the PCB, so I am using stencils. Do some solder pastes stick better than others?

I have been using Kester 256 for years, hundreds of boards done, good no-clean paste, no issues with non-sticking in about 1 year from purchase date, and that is when I finish the last year supply and buy a new one.

I have a syringe of Kester 256 from cml, I will give it another try (now using small jars which work better than syringes with stencils)

I wouldn't mind to buy a compact power dispenser but the ones I saw require shop air pressure which I don't have at home.

[coflynn]

I wouldn't mind to buy a compact power dispenser but the ones I saw require shop air pressure which I don't have at home.

It is well worth getting a small compressor. I struggled to use paste reliably with a syringe, but once you get a proper dispenser you can use even year-old crappy paste and still get reliable dot sizes for placing resistors etc. You can see it running here:

The small compressor is loud as hell unfortunately when charging, so if you live in an apt. you can't do anything late at night! Larger/more expensive units are supposed to have nicer/quieter motors, but that one was $50.

As a side-note, if you haven't seen the Silhoutte Cameo it's a good investment for quickly making stencils, which is also very useful for solder paste dispensing (see http://hackaday.com/2012/12/27/diy-smd-stencils-made-with-a-craft-cutter/, I made some more recent notes about what worked for me at http://colinoflynn.com/2014/11/smd-solder-paste-stencil-creation-with-silhouette-cameo/ ).

[rx8pilot]

The small compressor is loud as hell unfortunately when charging, so if you live in an apt. you can't do anything late at night! Larger/more expensive units are supposed to have nicer/quieter motors, but that one was $50.

I got this gem from Amazon. VERY quiet - enough to have right next to you and not be bothered.
http://www.amazon.com/California-Air-Tools-CAT-1650A-1-6-Gallon/dp/B00889ZYEC/ref=sr_1_7?s=hi&ie=UTF8&qid=1428254576&sr=1-7&keywords=california+air+tools

[coflynn]

I got this gem from Amazon.

That's good to know they exist! I run mine in another room, with ear protectors on. It's the crappiest cheapest model, so has a tiny piston and motor which of course means is super-loud.

I see they are even on Amazon Canada, unfortunately with recent changes in exchange rate it's not a great value ($250 CAD) for how often I use it right now...

[SteveyG]

I wouldn't mind to buy a compact power dispenser but the ones I saw require shop air pressure which I don't have at home.

It is well worth getting a small compressor. I struggled to use paste reliably with a syringe, but once you get a proper dispenser you can use even year-old crappy paste and still get reliable dot sizes for placing resistors etc. You can see it running here:

That's a nice little dispenser. I guess I need to start looking for something like that in the UK, I already have a silent compressor under the bench for my desolder tool.

Nice channel by the way, I've just subscribed - I see you also have the Metcal HCT2-120. I didn't find I have to have mine at 450°C though.

[M4trix]

I'm going to need a relatively small applicator

You heard the man. He doesn't need the whole machinery (quiet or loud compressor).   

[skyjumper]

I have never tried the needle approach, since I have hade great luck with caption stencils. There are several people who will cut them for you from your Gerber files rather cheeply. One guy even included a free plastic squegie. This method speeds application so you have more working time for placement. Most important thing whether you use stencil or a syringe is to make sure your board house puts soldermask between the pads on all components, even those with fine spacing. Not all do and I learned this the hard way.

[mikeselectricstuff]

As a side-note, if you haven't seen the Silhoutte Cameo it's a good investment for quickly making stencils, which is also very useful for solder paste dispensing (see http://hackaday.com/2012/12/27/diy-smd-stencils-made-with-a-craft-cutter/, I made some more recent notes about what worked for me at http://colinoflynn.com/2014/11/smd-solder-paste-stencil-creation-with-silhouette-cameo/ ).

I bought one of these a while on a bit of a whim - not yet had a serious play with doing stencils, but for a fairly simple job  a while ago, I just exported a DXF from my PCB software & it cut it pretty well. Bit of pain clearing all the holes - sticky tape got most of them but needed some manual poking-out.

[zapta]

I bought one of these a while on a bit of a whim - not yet had a serious play with doing stencils, but for a fairly simple job  a while ago, I just exported a DXF from my PCB software & it cut it pretty well. Bit of pain clearing all the holes - sticky tape got most of them but needed some manual poking-out.

Can it so let's say 0.5mm pitch qfn?

I tried once at work to cut a stencil with a laser cutter but it was not fine  enough and I just got one big hole.

[mikeselectricstuff]

I bought one of these a while on a bit of a whim - not yet had a serious play with doing stencils, but for a fairly simple job  a while ago, I just exported a DXF from my PCB software & it cut it pretty well. Bit of pain clearing all the holes - sticky tape got most of them but needed some manual poking-out.

Can it so let's say 0.5mm pitch qfn?

I tried once at work to cut a stencil with a laser cutter but it was not fine  enough and I just got one big hole.

It would probably need some careful tweaking to get that fine.
Should be doable on a laser cutter though - I buy lasercut plastic stencils which do 0.5mm pitch just fine. There was an articke on Hackaday a few days ago about lasering stencils - the trick is to use raster-scan engrave mode rather than vector cuts

[coflynn]

Can it so let's say 0.5mm pitch qfn?

See attached image - Spartan 6 LX9 TQFP footprint, which is 0.5mm pitch but QFP. This is after I've used the stencil once, and the caps around the side are mostly 0402 size. This is with zero tweaking to file... open gerber in GUI, hit buttons to start cutting. I've cut 0.5mm QFN stencils w/o issue before but don't have any around right now.

Only thing to change is cutting pressure depending on the material, but there is a script which makes a bunch of test cuts. Once you dial that in shouldn't need to tweak.

You might have to shrink apertures bit of course depending on thickness of material you use, but that would be the same for anything I assume. I'm using Eagle so that's easy to do when generating the stencil layer.

Overall I was shocked how well it works, especially from what is a machine for crafting. I had little desire to spend time screwing around and just wanted stuff to come out ready to use, which is basically how it worked for me. The material is key... I mention in my link what I think was 3 mil Mylar Drafting Film from the local craft store worked far better than the transparencies other people seemed to recommend.

Bit of pain clearing all the holes

Might need more pressure to improve cut through? Alternatively a different material... I've had great luck with drafting film (mylar). Almost all the cut-outs stick to the cutting pad, which can be scraped off easily.

HCT2-120...I didn't find I have to have mine at 450°C though.

Good to know, thanks for the info! I'll have to play around with lower temps then... had trouble getting things to quickly flow at much lower than say 400. I might have just been impatient however! I think I was overall hoping to magically faster reflowing as their demo video seemed to show, so might have been partially psychological on my side why I wanted it faster ;-)

[zapta]

There was an articke on Hackaday a few days ago about lasering stencils - the trick is to use raster-scan engrave mode rather than vector cuts

Found it, thanks,  http://hackaday.com/category/laser-hacks/  and it leads to this https://lowpowerlab.com/blog/2015/03/27/laser-etching-smt-stencils-tutorial/ .I will try the engraving method.

When I used the laser cutter I just tried to cut through. When it failed I just assumed that oshstencils.com, which I often use, has a finer laser.

BTW, I prefer 5mil stencils over 3mil (oshstencils supports both) because they print more paste.

[rx8pilot]

I just got some PTFE/Teflon lined needles today. What a HUGE difference! I was able to get the paste through a tiny 25ga needle and successfully hand solder a .4mm QFN without the usual bridges. That is a big upgrade for me. Love these things.

It requires way more pressure than practical by hand, so a dispenser is mandatory for these tiny needles. Being able to do small components without a stencil is fantastic though.

[zapta]

I just got some PTFE/Teflon lined needles today. What a HUGE difference! I was able to get the paste through a tiny 25ga needle and successfully hand solder a .4mm QFN without the usual bridges. That is a big upgrade for me. Love these things.

It requires way more pressure than practical by hand, so a dispenser is mandatory for these tiny needles. Being able to do small components without a stencil is fantastic though.

Where did you get them?

Apropos solder bridges, I found the beep mode of this product http://amzn.com/B0032JOAWA to be very useful for testing for  solder bridges. Also, if two adjacent pads are intended to be connection, I make the connection outside of the IC's outline so it's visible.

[rx8pilot]

Where did you get them?

McMaster Carr  75165A135
http://www.mcmaster.com/#catalog/121/3456/=wn2ots