Author Topic: Most appropriate solder paste for home/hobby use  (Read 3717 times)

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Offline mark03

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Most appropriate solder paste for home/hobby use
« on: January 03, 2018, 06:44:43 pm »
I am finally ready to discard my four-year-old (!) solder paste and buy some new.  I apply with an ordinary syringe and disposable plastic dispensing tips, no stencil.  Any opinions on the best choice of [tin-lead] paste for home use?

Criteria:

* Long shelf life.  This is by far the most important to me, as I never manage to use all of the paste before it goes bad.  It's also a given that I will use the paste well beyond its spec'ed shelf life, but presumably a longer official shelf life would translate into a longer "hobby-useful" shelf life.

* Low viscosity.  With my last paste (FCT NC676) it was difficult to get the tiny bead I wanted out of the syringe, without also risking blockages at the tip, even when the paste was fresh.  The lower the viscosity the better.

* Clean-up.  I have a choice of no-clean or water-soluble, but only have experience with the no-clean.  Is it easy to clean the water-soluble stuff with a gentle toothbrush?

I have a local source for FCT pastes.  NC676 is what I used last:
https://fctsolder.com/wp-content/uploads/2017/03/NC676.pdf
There is also WS159:
https://fctsolder.com/wp-content/uploads/2017/03/WS159.pdf

Their web site makes it sound like the water-soluble WS159 might have a longer shelf life, but the actual data sheets have identical boilerplate text :palm:  The WS159 is also listed as having a higher viscosity.

Suggestions?  Thanks.
 

Offline rstofer

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Re: Most appropriate solder paste for home/hobby use
« Reply #1 on: January 03, 2018, 07:12:35 pm »
I just can't get excited about the $16 it costs for a syringe full of solder paste.  When it gets too hard to push through the needle, I buy another one.  When it comes to boards that I will reflow, some small portion of $16 is just chump change.

http://www.howardelectronics.com/soldering/soldering-accessories/solder-paste-and-flux/qualitek/p615d-013-8840i-qi-qualitek-sn63-37-solder-paste/
 

Offline tooki

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Re: Most appropriate solder paste for home/hobby use
« Reply #2 on: January 03, 2018, 10:46:22 pm »
I use the syringe of 63/37 solder paste from MG Chemicals that I bought on Amazon. I keep it in the fridge.

Anyway, I strongly advise against water-soluble. If for any reason you fail to flawlessly remove every trace of the flux residues, then you risk corrosion down the line. (Water soluble fluxes are acids that are corrosive at room temperature. No-clean and rosin fluxes are also acids, but which are only active at soldering temperatures.)
 

Offline mark03

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Re: Most appropriate solder paste for home/hobby use
« Reply #3 on: January 04, 2018, 02:56:45 am »
I just can't get excited about the $16 it costs for a syringe full of solder paste.
This is already progress.  I was not aware of *any* mail-order source which would condescend to ship paste in a non-refrigerated, non-express manner.  The usual problem is that shipping costs more than the paste itself.  Looks like $3 USPS is an option for Howard Electronics :-+
 

Offline Bud

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Facebook-free life and Rigol-free shack.
 
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Offline helius

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Re: Most appropriate solder paste for home/hobby use
« Reply #5 on: January 04, 2018, 03:57:56 am »
Are you using a manual plunger to dispense from the syringe?
There are dispensing systems that run on compressed air, and some that use a DC motor. It is much easier to get a controlled bead with these, even if the viscosity is high.
https://www.eevblog.com/forum/reviews/dm-dispenser-now-available/
https://www.eevblog.com/forum/reviews/solder-pasteflux-manual-syringe-applicator/
https://www.i-extruder.com/en/
 

Offline blueskull

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Re: Most appropriate solder paste for home/hobby use
« Reply #6 on: January 04, 2018, 04:01:48 am »
Since you live in the US, there is a "247 Solder" on Amazon that repackages big player's products into small syringes (SnPb and SAC305 from Kester, SnBi from AIM, low temp chipquik clone is their house product).
I'm happy with their products so far. For $11 each, discarding annually is not expensive, and they work well even under room temp storage, though I don't use them in professional works where reliability matters.
I have access to refrigerated EFD and Indium solder pastes at work, but I use those small 247 Solder syringes at home for hobby.
Frankly speaking, there's not that much a difference.
 

Offline evb149

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Re: Most appropriate solder paste for home/hobby use
« Reply #7 on: January 04, 2018, 04:09:39 am »
One thing about common lead free pastes (at least ones used in mass production) is they tend to flow less than the leaded pastes.  And they melt at higher temperatures also of course.
The higher temperature melting may be less convenient for toaster oven / skillet / manual soldering, but if you're stencil printing the paste and reflowing it it *may* be helpful to have paste that "stays put" on the pad better than flowing all over the place long before you even get up to reflow temperature.
In theory the lower flowing pastes should be less likely to flow through places they're not desired to like small to medium-small vias / holes etc.

That said I haven't tried stencil printing a significant variety of lead free pastes for DIY PCBs so I am not sure what range of flux / paste flow ranges there are for DIY type pastes since there are many varieties. 

But I have seen quite a few "runny" Pb/Sn based pastes (which admittedly can usually work fine if you don't get unlucky and have the excess form solder bridges).  I'd worry more about BGA/QFN type footprints where you can't inspect for bridging and you're not unlikely to have excess / smeared paste around, and the vendor's solder mask design rules probably don't mask between fine pitch pads anyway, so any advantage due to the paste / stencil / reflow is perhaps nice in theory.

 

Offline blueskull

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Re: Most appropriate solder paste for home/hobby use
« Reply #8 on: January 04, 2018, 04:16:04 am »
But I have seen quite a few "runny" Pb/Sn based pastes (which admittedly can usually work fine if you don't get unlucky and have the excess form solder bridges).  I'd worry more about BGA/QFN type footprints where you can't inspect for bridging and you're not unlikely to have excess / smeared paste around, and the vendor's solder mask design rules probably don't mask between fine pitch pads anyway, so any advantage due to the paste / stencil / reflow is perhaps nice in theory.

Don't open paste mask on BGA pads. Spray some liquid flux before stencil printing, then solder the BGAs without paste, it is recommended when you don't have confident on BGA solder paste printing.
This only works for ENIG and tin plated boards for apparent reason, any warping can cause big trouble for this, and less available flux makes silver boards unusable.
 
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Offline tooki

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Re: Most appropriate solder paste for home/hobby use
« Reply #9 on: January 04, 2018, 04:37:54 am »
Don't open paste mask on BGA pads. Spray some liquid flux before stencil printing, then solder the BGAs without paste, it is recommended when you don't have confident on BGA solder paste printing.
This only works for ENIG and tin plated boards for apparent reason, any warping can cause big trouble for this, and less available flux makes silver boards unusable.
What? Can you reword all that? It doesn't make sense, though I can tell it's useful advice, whatever it is!
 

Offline blueskull

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Re: Most appropriate solder paste for home/hobby use
« Reply #10 on: January 04, 2018, 04:45:10 am »
What? Can you reword all that? It doesn't make sense, though I can tell it's useful advice, whatever it is!

Some component manufacturers recommends not to deposit solder paste on their BGA chip footprint due to the concern of bridging. Instead, they recommend to solder the chips with just heat with no paste, just use the solder balls under the chip themselves.

In reality, I found adding some flux helps to hold the chips down and helps to wet the surface.
 

Offline tooki

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Re: Most appropriate solder paste for home/hobby use
« Reply #11 on: January 04, 2018, 09:46:07 am »
Oh, gotcha. But why would anyone even think to apply solder paste to a BGA?? The whole point of the balls is that they alone provide the solder. Flux, of course, is critical since it’s a reflow operation.
 

Offline blueskull

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Re: Most appropriate solder paste for home/hobby use
« Reply #12 on: January 04, 2018, 09:51:13 am »
Oh, gotcha. But why would anyone even think to apply solder paste to a BGA?? The whole point of the balls is that they alone provide the solder. Flux, of course, is critical since it’s a reflow operation.

BGA balls are designed to have a certain stand off height for inspection and stress relief. With insufficient solder, you will have the parts witting on less solder, hence shorter distance for mechanical stress buffering. You can get around with shrinking pad side to have the balls taller instead of fatter, but then you reduce effective solder interface area, hence reducing reliability.

This is a reason why people use LGA sometimes -- they can sit very low, so stand off height is not that important anymore. Of course, the extra stiffness increases stress force, but then most LGA packages have ridiculously large total solder area, so per area pressure is fairly low. This effectively transfers deforming to PCB, instead of solder joints. This is also how QFN manages stress.

But of course, BGA is still useful for the high density and good self aligning. You can't do dog-bone with LGA, and mis-aligning of an LGA package can easily cause bridging.
 
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Offline TheDane

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Re: Most appropriate solder paste for home/hobby use
« Reply #13 on: January 04, 2018, 10:10:23 am »
Chip Quik has a two part solder paste solution.
https://www.digikey.com/en/product-highlight/c/chip-quik/patent-pending-two-part-mix-solder-paste

It has a long shelf life (24 months), and comes in various sizes and compositions.

I do not know how well it mixes with other fluxes, to 're-flow' the paste.
 

Offline SimonD

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Re: Most appropriate solder paste for home/hobby use
« Reply #14 on: January 04, 2018, 01:56:47 pm »
What about the GC10 Henkel / Loctite ?
I hear good words in the forum ...
 

Offline tooki

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Re: Most appropriate solder paste for home/hobby use
« Reply #15 on: January 04, 2018, 01:59:12 pm »
What about the GC10 Henkel / Loctite ?
I hear good words in the forum ...
Given that Henkel bought Multicore (which has a stellar reputation) and has been little by little rebranding the Multicore products as Loctite, I’d expect it to be top-notch.
 

Offline helius

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Re: Most appropriate solder paste for home/hobby use
« Reply #16 on: January 04, 2018, 08:28:29 pm »
BGA balls are designed to have a certain stand off height for inspection and stress relief. With insufficient solder, you will have the parts witting on less solder, hence shorter distance for mechanical stress buffering.
Yes. BGA mounting normally uses both paste stencil printing and solder ball positioning. See this video of a combination stencil and ball machine from Japan:
 

Offline tooki

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Re: Most appropriate solder paste for home/hobby use
« Reply #17 on: January 04, 2018, 09:13:19 pm »
Ignoring reballing of salvaged BGAs, I thought that virgin BGAs came with solder balls attached, and that then they were simply fluxed and reflowed to the PCB. Are you saying that virgin BGAs get solder paste on the PCB, too?
 

Offline wraper

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Re: Most appropriate solder paste for home/hobby use
« Reply #18 on: January 04, 2018, 09:54:20 pm »
Ignoring reballing of salvaged BGAs, I thought that virgin BGAs came with solder balls attached, and that then they were simply fluxed and reflowed to the PCB. Are you saying that virgin BGAs get solder paste on the PCB, too?
Usually small amount of paste is applied to the pads. Some BGA chips actually have metal coated polymer core balls instead of simple solder balls and they require solder paste.

 
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Offline blueskull

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Re: Most appropriate solder paste for home/hobby use
« Reply #19 on: January 04, 2018, 10:31:31 pm »
Ignoring reballing of salvaged BGAs, I thought that virgin BGAs came with solder balls attached, and that then they were simply fluxed and reflowed to the PCB. Are you saying that virgin BGAs get solder paste on the PCB, too?

Yes, and always in mass production where stencil printing is reliable.
 
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Offline Corporate666

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Re: Most appropriate solder paste for home/hobby use
« Reply #20 on: January 04, 2018, 10:37:25 pm »
CML Supply, Kester EP256  :-+

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

Buy this.

I have used various different leaded (and some lead free) solder pastes from AIM, Sparkle, Chipquick, Loctite/Henkel and others - and nothing comes close in my experience to EP256.  EP means Easy Profile and it is aptly named.  It is SO forgiving. 

I have pasted boards that sat around for three, four or five days before components got placed on them - no problem.  I've had jars of the solder paste sitting around for months unrefrigerated that performs the same as brand new product.  It has almost no residue, parts reflow and center perfectly on pads, I never have issues with tombstoning, and it has a great consistency that is great for either silkscreening or syringe dispensing. 

It's not always the most popular person who gets the job done.
 
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