What Happens When the Ink is Beyond the Shelf Life

[Bichengliu]

I started printing with the V1 when it arrived back in September or October, and I think I read somewhere that the shelf life of the ink is about 6 months. I recently tried printing circuits with my ink, and the calibration of the dispenser started to draw very faint lines on my PCB material, despite the flow rate of the ink being perfectly adequate when I twist the nozzle.

Does the ink start to dry out more quickly, or am I just using a board that's a bit too slippery for my nozzle size?

[mewertow]

Hi @Bichengliu,

The ink will thicken up over time, and eventually this will affect the printing quality and electrical properties / solderability. This could very well be what you're seeing. Can you check the lot number of the conductive ink? It'll be written on the cartridge.

Another consequence of expired ink is that the seal in the piston may be broken due to the increased pressure required for dispensing. Check to see if there's ink in the cartridge barrel, behind the piston.

However, it could also be that some ink has dried out in the nozzle - I'd suggest trying to purge some ink manually for about 10s. You can also try cleaning out a nozzle if you don't have a spare to test out - see the recent comments in this thread.

• Matt

[thormj]

I actually got 8 month old ink to work (stored horizontally in a refrigerator @ 33), but I had to clean out the nozzle with acetone first. Be sure to let it dry out completely before loading and trying to print, and while the nozzle is off squirt out a 1/8" bead and wipe it off so the fresh ink is "at the tip."

[Bichengliu]

I managed to get everything to work, it turns out that it was the nozzle which was not working properly. I think I will also be cleaning the nozzle tip with acetone to try to make the individual tips last a bit longer. I'm not entirely sure how frequently to clean it out, but every few printings should work.

I also realized that letting the cartridge warm up a bit, and letting the ink flow helps. I am unsure if this is impacted by the age of the ink, but it has helped with better printing.

Bicheng

[cborn]

@mewertow I see the limited shelf-life of the inks as being a particular concern given the way many of us use our machines. In a production environment this is never going to be a problem, but in a small general purpose workshop like mine it could easily be 6 months or more between PCB prototyping jobs, then when one comes up the client wants it done quickly. Most of my boards are in production, and the V1's main use would be in paste application for repair/replacement jobs, but I do have a few small test boards waiting to be started, and probably a burst of experimentation on some new projects in 2-3 months time.

I figure you are the experts on the chemistry of the inks and will know the mechanisms causing deterioration and how best to stabilize them, can you share some of that here? The ones that first come to my mind are:

1. Loss of volatiles.
   This happens for example with petrol, which "goes off" over time. You can add stabilizers to increase its life, but keeping in in a completely sealed container extends it indefinitely.
2. Separation of constituents.
   This happens with the normal solder paste I use. Over time the liquid and solid particles separate, and I get a thin liquid coming out of the nozzle and thick clumping particles left behind. If I stir it up thoroughly I can generally get some more use out of it. (Think homogenization for long-life milk)
3. Chemical reactions
   The material "goes off" due to chemical reactions between components, or exposure to external elements. Generally some sort of stabilization agent can be used to retard this process. Refrigeration may slow it, better sealing in the case of oxidation, heating to drive off moisture, etc.

Knowing the cause, it would be great if you could develop a "long life ink/paste" protocol!

[mewertow]

Hey @cborn,

The main limiting factor in the useful lifetime of the ink is chemical reactions between the components. Evaporation of solvents is less of a concern if the ink is stored properly (capped and upright at 4-10C), but over long periods can cause the ink at the tip of the nozzle to dry out - to help prevent this from happening, I generally recommend purging a small amount of ink every few weeks to maintain fresh ink in the tip.

You are right that there are some approaches which can slow down the progress of chemical reactions in the ink. However, one of the realities of designing functional materials is that the quantity and properties of every component will have an impact on the final properties of the ink. The formulation we currently use is a careful balancing act of components used to achieve excellent solderability, conductivity, and mechanical properties of the cured ink, and the proper rheology so that ink can not only be dispensed easily, but maintain its shape once dispensed.

The procedure that we currently recommend (store upright and capped, refrigerated at 4-10C) is the best way to ensure that the shelf life of the ink will be maximized. Almost all materials (even solder pastes) have an expiry date, and good storage practices are the best way to maintain the maximum shelf life.

Expiry of the conductive ink is a complex process, and it is difficult to predict exactly when a cartridge of conductive ink will stop performing suitably. The expiry date we list on the cartridges is based on our experience and testing thus far, but how long the ink will last after the expiry date depends on the storage conditions. For example, check out my post on this thread - the ink I tested was stored in a sealed cartridge at recommended conditions, and it both printed and soldered well past the expiry date.