Phil Zarrow: Brook, we've been talking about process issues with solder paste. Let's talk about care and handling. We receive our solder paste from shipping and handling, what's next?
Brook Sandy-Smith: Well, you want to get it into refrigeration as soon as possible. We ship our solder paste cold and in a cooler because we are intending for it to arrive to you at room temperature. We don't want to ever have it get warm. It would be a red flag if your solder paste arrived and you went to put it in the refrigerator and it felt warmer than room temperature, more than 100 degrees Fahrenheit. Otherwise, just store it in the refrigerator. For cartridges, make sure that they're stored tip down for ease of dispensing them later when you go to use it.
Phil Zarrow: Stuff happens. Let's say the solder paste was delayed in transit, held up in customs or in a trunk went through a very hot climate, we don't know what temperature excursions it might have experienced in transit, what are some of the symptoms that perhaps a solder paste may have been jeopardized?
Brook Sandy-Smith: We've done a lot of testing on this, Phil. I've tested lots of different solder pastes to see where that point of failure is, and usually when we have performance issues the paste looks different somehow. When you open up the jar of paste, it's normal to see a little bit of flux separation, but if it was really extreme, that would be a red flag. If you saw crustiness on the edges or dryness, that would be a red flag for you. Generally, with a jar of paste, you can just stir it up with a plastic spatula, nice and gentle. I wouldn't recommend using some sort of equipment to stir it, like a paint stirrer or something, you would want to steer clear of that.
If it's that extreme and you need to stir it that hard, then there must be something wrong with the solder paste, honestly. A plastic spatula should do it and with a cartridge, you should just be able to squeeze it right out, especially if you've been storing it tip down as recommended.
Phil Zarrow: Now, let's talk about the interval: it's in the refrigerator, it's been treated properly, from refrigerator to the printer stencil, what are we talking? Let's talk about conditioning.
Brook Sandy-Smith: We usually sell 500- or 600-gram containers, so just take it out of the refrigerator two or three hours before you're going to use it, and allow it to come up to room temperature – just naturally in contact with ambient room temperature. The only way to speed it up would be to use a water bath at room temperature. That might speed up the heat transfer, but we never recommend taking out a container of solder paste and putting it on a heater. Don't put it on your radiator next to your stencil printer or do anything to try and heat it up more quickly.
Phil Zarrow: I mean, it's a very massive amount, logic would say you can't just heat it like that, but also, with regard to conditioning times, it's going to vary on the volume of the jar, and hence the mass of what's inside. What we like to do is put a thermocouple in and see how long it takes that particular container size to come up to ambient and then we know. If I'm using 500 gram, 600 gram, 1,000 gram, whatever, that we know that but you're right. It has to come to the ambient temperature or it’s not going to print well.
Brook Sandy-Smith: Yeah, if you have some special container of solder paste, you might want to come up with your own rule of thumb on that, just like you're suggesting.
Phil Zarrow: Now, we're on the stencil, let's talk about pot life, stencil life, what have you found with regard to longevity of the solder paste usefulness or the solder paste on there.
Brook Sandy-Smith: I've done a lot of testing with Indium8.9HF. In this kind of a category it really stands out as far as how long it lasts in the refrigerator, how long it lasts at room temperature, and especially how long it lasts on the stencil. You know, a normal production day will take eight hours, or that's one shift, and I always verify that our paste is going to last that full eight-hour shift. I have a procedure where I stretch out the number of boards that we're printing and I really make one bead of paste last the whole day. That's definitely verified. With Indium8.9HF, it stands out because I can even leave it over the weekend.
Now that wouldn't be a best practice, you wouldn't want to leave exposed solder paste on a stencil for a weekend, but that just gives you that much more confidence that when you do run into the second shift with the same bead of solder paste, you'll still be okay and you'll still be getting the same paste transfer that you were seeing at the beginning of the shift.
Phil Zarrow: Now another situation is, I've been doing my production run, and I've only used a partial amount of the volume of a container, be it a cartridge or a jar, how do I store that? I certainly don't re-refrigerate it, but how do I store it?
Brook Sandy-Smith: No, I would never put it back in the refrigerator. When you receive the solder paste, it should go directly into the refrigerator and then once you take it out to use it, it should never go back into the refrigerator.
Each solder paste is a little bit different, how long it maintains the same properties when it's stored at room temperature. With Indium8.9HF, it has a month shelf life at room temperature, so that should just give you the confidence, you take out the jar and you're not sure whether it's been there three or five days, you're sure that it'll be okay. Now best practice wouldn't be always leaving your jar out for 30 days and then using it, right?
Phil Zarrow: Right.
Brook Sandy-Smith: We extended the shelf life on Indium8.9HF to really give you that confidence factor that when something doesn't go perfectly or when a jar of solder paste is just out and being used and it's not in this window of our usual best practices, that it'll still be okay.
Phil Zarrow: I want to remind you, we're talking about having that container closed, not open, meaning a jar with a lid on it or a cap on the cartridge.
Brook Sandy-Smith: Yes.
Phil Zarrow: Brook, we can find more information on these best practices on www.indium.com?