SparkFun Forums

[riden]

How about offering small quantities of lead-free solder paste (~1cc) packaged in a diabetic or 21 gauge syringe with the needle cut off at 1/4 inch and blunted. I read a post about an amatuer radio group that offers a lead paste paste for $5 per syringe, but you need to pick it up in person because of the restrictions of transporting hazardous materials (lead). I would think a lead-free product would be free from those restrictions, and I would like to move to lead-free anyway.

This product would be a nice complement to the breakout boards us nubies to SMD like to use. Having this option would minimize the cost of trying out reflow techniques and would help ensure that the paste won't go bad if you only need a little from time to time.

[FESCSteve]

May be cost effective for someone to purchase the larger 600-700 gram cartridges and fill smaller syrenges for hobby and low volume use. I may personally look into it if there is enough interest.

As for lead free alloys - if Spark Fun is going to offer this, pick an SnAgCuBi alloy. Reflow at 225C for good results.

Steve

[riden]

I think that the interest is there, but people might not know that such options exist. I have two project boards I bought that had runs of 800-1000 units each and they suggested hand soldering (small potatoes, I know, but that was just two kits).

As reflow techniques using inexpensive household appliances are published, people are "seeing the light" (as another topic stated) and hobbiests will be looking into ways of getting into the action without having to bother with large quantities of paste that could go bad in the fridge. If the overhead and hassle of packaging and shipping aren't prohibitive, getting the word out should generate a decent flow of orders.

[Philba]

what kind of syringes do people use? I would consider buying a quantity, stuffing some syringes and selling a few.

what i really want is an automated paste dispensing CNC-bot. just the right daub on each of the sm pads. maybe someday...

[riden]

One article that says that diabetic syringes worked best (smallest bead) but they clogged up too easily. The one I received is a 21 gauge, 3mm B-D syringe (#305273) with 1cc of Kester Easy Paste 256. The needle was cut off at 1/4 inch and has been blunted.

The thing that I'm concerned about is any restrictions on the sale and transport. In Illinois, I'm not permitted to even purchase these syringes without a medical prescription.

[FESCSteve]

Syrenges and tips are not a problem - I have sources for them in bulk. I think the most common are 10ml 'EFD' syrenges for automated equipment, but that amount would last someone quite a long time as a hobby.

Filling them can be a but combersom though. EFD does make equipment for that purpose.

Steve

[SOI_Sentinel]

It's still cost prohibitive from a shipping standpoint. Solder paste, especially repackaged outside a dedicated facility, does not live well when transported through who knows what climates. Digikey's lead free solder paste must be sent next day air or 3 day express IIRC. Void-free is important if you want to be able to control the flow rate.

As for syringes, I personally use the professional Luer Lok style. I've looked through Wassco for stuff like that before:

http://www.wassco.com

Low cost Kahlnetics: Roughly $10 for 20 syringes (dunno if they come with plungers). $8 for 50 industrial needles.

I recommend the Luer Lok system as the needles are held on with a half twist, so are easily switchable and they also make locking caps, too. Looks like 3CC would be a good number.

[FESCSteve]

Yes, the locking mechanism is important to remember when dispensing paste. The Kahnetics brand are fairly decent and cheaper than EFD. Keeping the paste free of voids requires the use of filling equipment almost certainly. You couls make an adapter that will let you fill one type syrenge from another though - just keep the plunger in place while filling to avoid air poskets. You definately don't want to just stuff it in the backside if you don't want airpockets.

Yes, paste does have to be kept refrigerated and thus shipped overnight. The expense of shipping will be the majority of expense. If you could guarantee that the paste we not exposed to over 70F it would arrive in good shape as long as it's sealed though. But who can you trust?

Mostly the paste becomes oxidized and the individual solder spheres will not form a complete solder joint and you'll get solder balling and perhaps poor wetting. There are tests that can be performed to test for oxidation and wetting, but it takes some of the paste to perform that. It's easiest to just ship overnight with a cold pack. And no, it cannot be frozen eiither you you possibly ruin the rehology of the paste.

Lost of little things to worry about for sure

Steve

[riden]

Disclaimer: The following is from the point-of-view of a hobbiest and not one who will be using the product commericially. I could be dead wrong and, as always, your mileage may vary.

I'm not convinced that overnight shipping is required. My package arrived in good condition via USPS (63 cents of postage) but took 2 or 3 days to arrive. It now resides in my fridge free to pursue the freedom to bond in the future. As with most things, there are certain parameters that must be met for mission critical applications and may be relaxed for less demanding ones. Some would think that using a hot plate or toaster oven to reflow is insane, while many others have been succesfully doing it. All I know is that I was very grateful to be able to purchase a small quantity for my projects. As more data is gathered, we'll have a better idea of the results hobbiests can expect. I read one post where someone was using paste that was several YEARS old and put it in an ultrasonic cleaner to "revitalize" the suspension when he needed to use a little of it. Would I recommend this? No. But does show that the useful life for non-critical uses is probably much longer than is reported.

[Nutter]

Here's a collection of solder-paste syringe links with similar products to what you're looking for:
http://www.solder-it.com/solderpaste.asp ($6 for silver solder syringe of unknown size, and lead-free)
http://www.stencilsunlimited.com/solder_products.php ($16 for 35g syringe)
http://www.zeph.com/zephpaste.htm ($12.85 for 10cc/12g)
http://www.howardelectronics.com/amtech/nc500.html ($16 for 10cc/35g)

They're not as small as 1cc like you're looking for, but the prices aren't bad! The StencilsUnlimited paste is especially interesting as it doesn't require refrigeration, so normal post is no problem (except for the lead.. unfortunately only the solder-it one is lead-free).

[SOI_Sentinel]

Hmmm... Kester is a known product, but how do these other manufacturers stand up with their synthetic no refrig pastes vs something like Kester 276?

I'm also curious about whether it's just marketing between a 12gm syringe and a 35 gm syringe.

[MGP]

I just bought a 250 gram jar of the SynTECH No Clean paste from Stencils Unlimited a couple months ago. I assembled several prototypes with it and I actually thought it soldered (Hot Plate) better than Kester 276.

Very good results, I like it so far.

I'm going to be doing a couple more boards this weekend. I'll post back the results since the paste will have sat on the shelf in my basement workshop for a couple months. It's cool and dry there so I don't expect any problems.

[SOI_Sentinel]

I'm considering the 250gm jar myself now due to the cost difference and possibly filling a few 10cc syringes for my own use (I have samples I forgot about from EFD). Maybe I should consider building a PVC syringe filler. (sorry, mechanical engineer)

[FESCSteve]

Paste manufacturers guarantee a shelf life under ideal conditions (ie - 6 months from date of manufacture when kept under 70 Deg. F, etc). When we started with SMT manufacturing many years ago, we would purchase paste in jars. With a jar, you open it, mix it, taker out what you need and then close it up. Problem is that so much area is exposed to an environment that the manufacturer cannot design for (low humidity, high humidity, etc). So most companies built their operating procedures around disposing a jar after opening. In practice this is not really necessary if the jar has a plug that lets you displace all the air and reseal. We could use jars for many days before they would start to dry out. NASA specifies oxidation and wetting tests on pastes before use because of this problem.

We long ago switched to cartridges. We'll purchase dozens of 600-700 gram cartridges (like a big syringe) and store them in refrigeration at around 40 Deg. F for their shelf life of 6 months. When it comes time to use one, we take it from the fridge and dispense what we need and replace the cap. If necessary this paste can sit on the shelf for many days or even weeks wihtout refrigeration. We tend to use an entier cartridge within a couple of days though. I'm fairly certain that if we kept them in storage at 70F or less they would still perform as well as under refrigeration.

I guess what I am eluding to is that a syringe is a good method for storing paste in that the contents are really kept from the humid air. If kept under 70F and out of the open air, things should be fine. The problem being that you can't really trust shippers to guarantee the environment that the syringes will encounter. No matter the paste formula, needing refrigeration or not, there are limites on what temperatures the paste should be exposed to. If the stuff sits on the tarmac in Pheonix for a couple of hours and get to 100F, things may not be good when it arrives. We've received more than a few cartridges that were not properly refrigerated and the paste flux became liquid and leaked past the plug, changing the flux/metal loading ratio.

[riden]

Here's a collection of solder-paste syringe links with similar products to what you're looking for:
<snip>
They're not as small as 1cc like you're looking for, but the prices aren't bad! The StencilsUnlimited paste is especially interesting...

Thanks for the information. I had heard about StencilsUnlimited before and had considered ordering from them. I think I need to find a small network of hobbiests in my area and pool our resources. I don't mind a little expense, it is the potential waste that bothers me, I'll get over it!

Fabrication has come a long way from when I first got started 25+ years ago. I couldn't have imagined being able to layout my boards at home and have them made.