Solder Paste Dispensing

Community PCB Design
1

I’ve never assembled a pcb other than by hand soldering. So, I used big enough components spaced far enough apart to make that feasible. This time, I’m going to have to use a reflow technique.

I’m anxiously awaiting for my pcb to be shipped by BatchPcb and need to order paste and dispenser tools. I don’t think I want to mess with a stencil, since I’l probably just be doing one or two boards.

Is there a place where I can get a good paste, syringe, needle, i.e., one stop shopping for everything I need for hand dispensing solder paste?

I saw an earlier post on this forumn that make me think dispensing with a syringe might not be all that easy, yet I’ve seen tutorials and videos that make it look simple. So, I was hoping someone would recommend tools that are know to work (and a place to buy them).

I’ll be using a hot plate.

Thanks,

Dave Thomas

2

I use Warton Metals:

http://www.warton-metals.co.uk/index.html

3

Thanks, but I should have said in US.

Dave Thomas

4

I prefer solder paste stencils (eg Oharap’s Kapton stencils), but have had good results using the “needles” from inkjet refilling kits. They are a lot larger bore than normal hyperdermic needles. Small syringes (eg 2cc or 5cc) allow a reasonable amount of pressure to be applied.

I just got some of this solder paste (shipped from Hong Kong), and it works well (and cheap - only $3.57 inc shipping):

http://www.dealextreme.com/details.dx/sku.4711

I didn’t have any of the issues some of the reviewers reported…

5

You can get blunt needle tips from SmallParts. Get a variety of sizes to see what works best - I personally use 16-20 gauge.

6

Jameco has a paste, syringe, needle, and plunger kit for $20:

https://www.jameco.com/webapp/wcs/store … Id=2098208

That’s a decent deal for the tools plus 35g of paste. It will last a long time.

I also use the super cheap Dealextreme paste, along with some of their super cheap hypodermic syringes with their “injecting pinheads” instead of the tiny metal needle. However you very likely will need to thin out the Dealextreme paste with liquid flux in order to use it with a needle or a stencil, so every batch ends up a different consistency. Fine for hand built work though.

7

Thanks for the replies!

Yes, I saw several reviews on the Dealextreme paste indicating that the paste must be thinned to be useable. So, I’d have to figure how/where to get the thinner if I went that route.

I’m really stupid about the syringes the paste is shipped with. If I get a blunt needle with a “Luer” hub, will that fit? Or will I need something else.

The Jameco kit seems attractive, since I really just want to make sure I get everything I need to get the job done, instead of getting stuff then realizing I need something else. Except I can’t tell what size needle it has. If I separately order a couple of needles, will they likely fit the syringe.

Dave Thomas

8

I use the DX paste and it works fine. I would think the only reason you would need to thin it is if you want to use it with a needle. I use it un-thinned, but I haven’t used a needle, yet. I think it would be fine as is with a template. I’ve just been using some clipped leads to extract a bit a spread it where it’s needed, but I only use it on parts that I need to use it on like QFN’s. I don’t do a lot of boards and I can do 0805’s and such quick with an iron.

If you want to thin it, you just use standard flux and mix it in.

For this, I used it for the two chips only. Ones a QFN, the other is called something else, but it’s essentially a long QFN.

http://www.higginstribe.com/msp430/rf-n … to-002.jpg

http://www.higginstribe.com/msp430/rf-n … se-001.jpg

9

what can be used as a thinner for the paste?

10

99% IPA worked very well when I tried it.

11

Have a look at the comments on the dealextreme link I sent previously. Several people suggest this flux to thin the solderpaste:

http://www.dealextreme.com/details.dx/sku.20583

When I used the paste with a stencil I didn’t need to thin it, but the weather was pretty warm on the day I did it. In any case, you’ll want some flux for SMD work, and that stuff seems to work pretty well.

12

I’d use that flux if I wanted to thicken the paste. That’s a sticky rosin-based flux, not a liquid flux. I guess you could use some 99% alcohol to thin the flux first, but you might as well directly add the alcohol to the solder paste. I’ve tried it both ways. Too much flux in the solder paste will make it pop and crackle too much during heating and bounce your small components off the pads.

The flux itself is good though, I’d recommend picking up a few tubes if you’re already ordering paste. Don’t forget SKU 21947 and SKU 21573 as well, and some 6238 and 19919.

13

Ok, did the dealextreme thing, picked up the suggested extra items.

The prices seem almost too good to be true. And free shpping!

I ended buying a bunch of stuff.

Is the iso alcohol you can buy anywhere 99%, or is that special stuff?

Thanks,

Dave Thomas

14

davethomaspilot:
Ok, did the dealextreme thing, picked up the suggested extra items.

The prices seem almost too good to be true. And free shpping!

I ended buying a bunch of stuff.

Is the iso alcohol you can buy anywhere 99%, or is that special stuff?

Thanks,

Dave Thomas

DealExtreme free shipping is slow - you’ll be waiting about 3 weeks usually :slight_smile:

Finding 99% in an average store is harder, 90% can be found in most drug stores. Remember that alcohol is hygroscopic - if left open or exposed to air it will convert into about 70%.

15

DX is addictive. Get magnifiers and tweezers from there as well.

This magnifying lens is tinier than it seems, but is really nice and clear.

http://www.dealextreme.com/details.dx/sku.22831

Another one is focalprice.com Less electronics stuff, but I just got a big board of single sided copper clad from there and it looks pretty nice. Haven’t cut it up yet, though.

http://www.focalprice.com/CX069Y/Electr … ellow.html

DX takes about 2 weeks for me. Focalprice took like 3 and a half weeks, but it might be because I ordered over the new year.

16

Just a note that IPA (isopropyl alcohol) is NOT the same as ethanol. When most people say “alcohol”, they mean ethanol (ie, what’s in drinks, methylated spirits etc).

17

If you’re in a Safeway part of the country, then I know they do have 99% isopropyl. I have seen it at Target too. Don’t get 70% it’s next to useless.

18

Monday, BatchPCB shipped my boards. Since I knew I wouldn’t get the stuff I ordered from DealExtreme before I got the cards, I ordered the solder paste, syringe, and needle kit from Jameco as suggested in this thread. (Thanks!)

Received the pcbs today. But,when I tried picking up and placing those tiny SuperSOT6 parts with the tweezers, it was OMG! What was I thinking! This is impossible!!

It was a mess. Just grabbing the parts with the right side up was the first adventure. Then, the parts would always stick to the tweezers. I resorted to just getting them close, then pushing them into place with a pointy tool I have.

Ended up dragging parts through paste and making what looked like a total mess. But I said, WTH, I’ll try reflowing on the hot plate to see which parts reflow ok, so I could guage how much better I needed to get.

It was a thing of beauty! Watching that ugly gray mess turn shiny and the parts magically align was awesome! I never dreamed the solder dispensing could be so sloppy and the result still turn out well.

One of the SOT6 did skew badly, so badly the pins got soldered to the wrong pads. So, I removed it, use braid to clean the pcb and part pads, then soldered manually (wicking the bridged leads with braid).

Haven’t functionally tested the board yet, but I did beep out all the fine pitch leads and verified connections to the card and no shorts to adjacent component leads.

Anyway, this is probably “old hat” for most of you, but it was quite exciting for a newbie (at DIY pcb reflow)! Kudos to SparkFun for their great tutorials and other trememdous resources!

Finally, the question. Is it ok to reflow the card more than once? As an example, to straighten out the bad SOT6 while the solder was in the liquid state? Or is reflowing multiple times a bad idea?

Thanks,

Dave Thomas

19

I finally used the old ink jet cartridge refill syringe and used it with the DX paste diluted with some liquid rosin. Hit it with some hot air and it worked out really well. I might do that more often.

DX has syringes as well. I ordered a few. There’s only a few types in stock, though.

20

davethomaspilot:
Finally, the question. Is it ok to reflow the card more than once? As an example, to straighten out the bad SOT6 while the solder was in the liquid state? Or is reflowing multiple times a bad idea?

Exposing components to unnecessary heat cycles is usually not a great idea. While many components can tolerate it (especially passives), you run the risk of compromising the quality of your solder joints on other parts that you aren’t targeting. Solder can be contaminated much easier while in a molten state and odds are you won’t be applying flux to all the parts that don’t need repositioning. Without flux, you run the risk of forming cold solder joints in areas that were fine to begin with. I can’t promise that it will happen every time, but eventually it will.

This type of rework is where a hot air station comes in very handy but your manual rework with the iron and wick is just as good.

-Bill