Got dem rewetting blues

[DavidYon47]

I've been finding from day one that adhesion is a challenge. Less so with reflow so long as the flatness of the pad enables good surface contact (although if the pad isn't flat then even simple items like 0602 resistors can have a very fragile bond). I've struggled with through-hole hand soldering but have been able to squeak by more or less. That was with the old solder wire.

Am trying out the new wire and am completely striking out. I cannot get it to wet onto a pad to save my life. The pad may as well be mask as far as the solder is concerned. I've tried adjusting temperatures, more flux, less flux, no flux (for tinning the pad). Nope. The solder globs up on the wire but is seemingly repelled by the pad.

I've tried turning my iron as low as it will go (150C) and the solder does seem to just barely flow at that temp. But the pads from the practice board look as though I used too hot an iron (and I most definitely did not apply heat for too long: 15-20 seconds at the very most):

The pads in the pic look white but that's the fault of the lighting and smartphone pic. They are silver and well-burnished. But you can see the results of my failed attempts (this is only three of many more). I can get the pad to barely tin, if at all, and the solder simply doesn't fillet around the wire. The topmost attempt had looked like it might work but broke with the slightest bit of pull on the wire.

What gives? I am still using my original ink cartridge, but it dispenses well and seems to cure and burnish just fine. I'm finding that I almost always having to use a new nozzle, which is a bit frustrating.

I love the concept of this device, and the silver-on-green boards look way purtier than the milled copper boards I've been doing with my Othermill. But if the ink won't take solder, or if it requires such a gentle touch that an entire board is scrap due to one failed pad, then I really have to think hard about the amount of effort I can put into mastering it.

That said, it does work very well for paste dispensing, and would be worth keeping around just for that . But I have yet to experience a smooth end-to-end workflow using ink.

[DavidYon47]

If it's useful, I can hook up my USB microscope and get more detail. I have 12 other failed pads I can show (they look similar to the above but were done on my iron set to 200), and I can also zoom in on the virgin pads so you can assess the burnishing.

[mewertow]

Hey @DavidYon47,

The new solder wire is pretty forgiving, I'm quite surprised to see it's giving you problems - all the feedback we've received so far from using the new wire has been positive. The only things I can think of are:

1) Expired ink - Can you check the expiration date on the cartridge? Poor solderability and clumping (hence, nozzle clogging) are classic signs of expired ink.
2) Solder residue on the iron - If you've been using other solders with your iron, leftover solder on the tip can be a problem. Clean the tip thoroughly and coat with the new wire.
3) Flux issues - Are you using the flux we provided? This is a long shot, but it could be conceivable that a different flux could be causing problems.
4) Temp Calibration on the iron - It's also a longshot, but It's possible that the soldering iron temperature isn't calibrated properly. However, the new solder will work at temperatures from melting (140C) up to ~260C (for very melt times), so it would have to be way off.
5) Over-burnishing - Another one for the longshots category - it is possible to get poor solderability ink if it's been burnished to basically a thin film (<30um thick). Not really applicable to this case, based on the photo, but I thought I'd throw it out there for future reference.

Based on the symptoms, I suspect it's #1.

[mewertow]

One more thing - could you please report the lot # on the cartridge? We have samples here for tracking purposes, so I can try printing / soldering over here and see how it goes.

[DavidYon47]

Well, the ink is expired, though not by much, and it's been sitting in the fridge pretty much constantly as I haven't had a chance to get back to this since October.

1. So yeah, ink past expiration, but working pretty well otherwise.
2. I've pretty well retinned the iron, certainly by now after all this practice.
3. Ironically, switching back and forth between the new and old wire, the supplied flux is just death to the pads. Once the flux heats up and flows over the pads, they turn dull grey and absolutely will not take solder. I have better luck without it.
4. Possible, but I tested a pretty wide range.
5. As you said, unlikely.

What's interesting is that even with the expired ink, the old wire is working much better. I can tin the pads, and get a decent fillet. The problem is that hookup wire (at least solid) is just the wrong thing. You cannot bend the wire at all without applying torque sufficient to break the ink pad. You pretty much would need to have a header or connector that isolates the pad from torque (which for my current application isn't easy to do with the current constraints).

My next experiment would be with stranded wire, which should be more forgiving on the solder joint.

[DavidYon47]

Stranded definitely relieves stress on the joint/pad. It has its own challenges (tinning risks making it too thick for the hole), but is at least usable. Perhaps curing expired ink makes it overly brittle, but certainly for me and my current cartridge the solid wire was unworkable.

[mewertow]

I just got a chance to print a hand soldering test board with one of our samples of Lot 169551606. Considering the expiry date, I didn't expect it to work, but it soldered fine for me with the new solder wire & supplied flux - see below for image (forgive the poor quality, I needed to use my phone camera).

Not bad for 9-month old conductive ink! It did feel a bit thicker when dispensing, as you can see the infill is a bit choppy in places, but it went well enough. The top pad is soldered to some 22-gauge tinned solid-core hookup wire.

Considering the issues you're seeing, I'd have to guess that it's either:

1) Incomplete curing - Did you make sure to flip the board on the clamp ledges, with ink facing down? If so, did the entire bake step finish properly (reach 210C for 30 minutes)?

2) Conductive ink storage - The samples we have on hand here have been refrigerated since manufacturing, which will maximize the shelf life of the ink.

[DavidYon47]

I'll have to do another practice board, but I'm pretty sure the bake went ok. I'll take a screen snap of the temperature graph.

Agreed that it's expired, though mine has virtually been in the fridge the entire time except for some in/outs last fall. So is probably in nearly the same shape as what you had. I'm somewhat stunned that you had such luck with the new solder. As I said, the old solder is working fairly well even with the potential pitfalls I might be experiencing, but the new one is completely dysfunctional. So much so that I may take a short video of what happens when I apply flux then attempt to get the solder to wet the pad. Might be interesting for you to see what I'm experiencing..

Also interesting that you didn't have issues with solid wire. Which would be more likely to contribute to the ink pad breaking under stress, curing or the age of the ink?

A couple of side notes:

1. From here, I can't see the pic, get a broken link instead.
2. Unfortunately for my usage pattern, which is low-volume, occasional use of the Voltera, the shelf-life combined with the price of the ink is something of a bummer. It's great that a cartridge has a fairly large capacity, but I was nowhere near using up that first one before its age became an issue. Is what it is I suppose.

[DavidYon47]

So of course the temperature graph scrolled off by the time I got back to the computer. But the red line showed a pretty wide (+/- 3C?) ripple, don't know if that mattered.

But I'm still flummoxed:

The bottom two rows, one in from the right, are the old solder. The pads tinned, I didn't even bother tinning the wire. Got a nice solid connection that survives bending the solid hookup wire to where it needs to point after it is soldered in.

The rightmost three on the top are the result of trying to tin the pads with the new flux and wire. The pads turn grey as soon as they are exposed to the iron when flux is on them. The new solder just stubbornly stays on the iron. I tried pre-tinning the rightmost two, and when I tried to solder the wire it would just clump to the wire and not stick to the fluxed pad. The next one over I tried using a different formulation of ChipQuick. Same deal.

The leftmost was an attempt to use the new wire without flux, just for kicks. I actually got the solder to stick to the pad. The problem there was that the slightest pressure on the wire broke it off the pad.

I don't know what to make of this. I know the ink is expired, but you folks were able to get it to solder, and I'm able to get it to solder with the older formulation. But the new solder simply hates the ink I have here. I almost wonder if it's the flux I got, though similar things happened with the Voltera-supplied flux as what I have here for SMD rework.

It's also worth noting that when I reflowed those tactile buttons from another post, I got a solid bond from both the expired ink and the (presumably) expired paste syringe. Despite the keystoning the buttons are pretty firmly attached.

[mewertow]

Hi David,

The +/- 3C ripple during baking is expected, and won't impact the curing quality. The expiry of the conductive ink typically presents in one of two ways - poor solderability, and thickening / clogging during dispensing, both of which are symptoms that you're experiencing. The conductive ink is well past the expiry date, after all.

The ink I tested with was from the same lot as yours, but was stored continuously in a sealed container at 4-10C, which means that it does not necessarily represent the same environment that your ink was stored and used in since you received it - rather it's an indicator of how ink could perform with good longterm storage.

The only thing I can recommend if you want to try to use this cartridge of ink is to try to use the Manual Reflow functionality to cure the ink at a higher temperature for longer - however, this is definitely experimental.

[DavidYon47]

Well, for what it's worth, the expired ink and paste gave good results when used with the original solder. Got nice fillets and a strong bond. My "simple" add-on to the Defusable Clock is now complete, except for a redesigned case and "visual accents".

[DavidYon47]

Bringing up an old topic while my soldering practice board bakes....

Back when I was struggling with this, I noticed that even just the flux itself seemed to corrode the pads when I tried to tin them. So...

1. Is it possible I'm using too much flux? If so, it would be hard to use less given the diameter of the nozzle and using a manual syringe.

2. Would tinning the pads without flux make any sense? Then put a tiny amount of flux on the pad once I'm about to do the final joint?

I've got lots of throwaway pin headers and a brand new practice board baking, so I'll be able to try lots of techniques. But any wisdom appreciated. It is such a sinking feeling to have invested a lot of time getting a board printed/populated only to have a pad destroyed by a through-hole part, since it's all but a given that you have to start over.

[DavidYon47]

Yay, finally getting the results that people have been raving about! When done correctly, the new wire really does flow and adhere much more easily.

For starters, I think my Solomon SL20 runs a little hot. I have to crank it all the way down to 150C and even then it melts the solder with ease.

I tried various things, but for pin-headers anyway, the most reliable thing is:

1. Tin (without flux) the pad on each side with small dab of solder. It will stick without flux, and the main purpose is to have solder on more of the pad so what once it starts to flow, there's solder where you want it. Otherwise you kind of have to drag the iron around the pad to get full coverage.

2. Put a small ball of flux on top of the pin.

3. Apply the iron to the pin, then drag down to the pad, covering as much surface area as possible, then apply the solder. At that point, if all is well, the solder just flows over the pin and pad, joining up with the dabs of solder that were already on the pad.

Maybe I couldn't find it, but it would be helpful if you folks were to post an updated soldering tutorial that demonstrates the new wire, because for best results it really is more steps.

I was able to get good joints by just putting on flux and then soldering ala copper, but I found that you really needed to move the iron around the pad to get full coverage and a good fillet. But that risks using an excess of solder and is a bit more hair-raising as you are applying heat to the conductive ink longer.

So I found the best technique was to tin the pad first. And it made a difference to tin it without flux. If there was flux then the solder tended to move around before you wanted it to. I also suspect that it increases heat transfer into the pad, which you want to limit lest you overcook it.

[jazozaya]

Hi @DavidYon47,

The office was in smiles when we heard you're finally getting good results soldering! I'm so glad you put up with it. I think a lot of people will benefit from your experience.

The tutorial was certainly developed with the old solder wire in mind, we are working on updating our website over the next few weeks so I'll see update the tutorial as well

Cheers