Super Dry’s Novel Approach to the Drying Process
Pete Starkey spent a few minutes at the Super Dry booth on the first day of the productroncica show, and chatted with old friend Rich Heimsch, who taught the old dog a few new tricks about the drying process.
Pete Starkey: Rich, it's great to see you here. Thank you for joining us.
Rich Heimsch: Very nice to see you again. It's good to do some work and catch up with old friends, which is what this show certainly offers to me. And it's significant also because of the difference between the U.S. and European markets in their attitude to moisture management.
Starkey: Rich, would you expand on those cultural differences?
Heimsch: The European market is simply more mature. It's considerably more advanced because they needed to worry about it much sooner.
Starkey: Would this relate back to 2006 and the introduction of RoHS regulations and lead free?
Heimsch: Yes. Overnight, virtually every component in a guy's shop needed to be watched, and a lead-free process adds one or often two MSL levels to every component. So, you could say it took them by surprise. They knew the legislation had a date, but there were a lot of other things to worry about first. “I need paste. I need re-flow.” That was a pressure thing. There was a bit of a surprise and that required some scrambling. And the founder of our company will say that it was that point in time that the business completely shifted gears. It was also a point in time where assemblers started to recognize that they needed to do things a different way. They needed to deal with the logistics of baking everything and then, “What am I going to do with it? Because the clock is restarting. Let's build something where I can store and reset the floor life in the same place.” That was the genesis of our ‘floor-life reset’ cabinets which have moved along significantly in capability over the years. I can recall bringing one to an APEX show, let's say eight years ago, and most of the people who came by said, "Really, what does it do and what would I need that for?"
Starkey: Could you just define your meaning of floor-life reset?
Heimsch: Restoring the safety of a component after it has expired, after it's been out in ambient atmosphere for too long. Exactly what traditional high-temperature baking was set to perform. Europeans then recognized that this baking induces oxidation and intermetallics and now felt it was time to deal with the solderability. They were baking more and more, a larger percentage of components, and creating more solderability related issues than they had before. Just by the numbers.
The low temperatures do not induce that oxidation. They greatly less induce intermetallic growth, and at the very low humidities, which just didn't exist when the 033 standard was written, accelerate the drying to where a 1% 60°C dry is faster than 90°C at atmosphere or even 90°C in a nitrogen oven. So, they kept going on from there. One of the things that we're doing now is offering in the machine the tracking of up to 20 different batches of parts and floor life being recovered with software to track them. Software to automatically calculate how much time it needs. If it's MSL3 and it's 1.4 millimeters in thickness and I'm at 1% at 40°C or 1% at 60°C, it will do the calculation for you. Hit start and it'll keep track of it and let you know when the different ones are finished. You can go in and out with more batches, with other batches, and that's where the recovery time that we talked about has played another role. Interestingly enough, the understanding and the take up of that low temperature baking is the most noticeable change in our U.S. domestic market as far as people who are doing it. I mean, still a lot of people feel they don't need to. Automotive, military, they have always known. We've had this conversation once before. You get an intermittent in your handset, it's an inconvenience. To have an intermittent in your airbag, your ABS, or your implant and it's another level of problem. So, I can't say across the board that the North American market is seven years behind, but in a generalized way, that's the case. These guys had to start somewhat sooner.
Starkey: Rich, can I ask just to explain in basic terms how the low-temperature desiccation, low-temperature moisture removal system works?
Heimsch: We create an atmosphere with virtually no moisture in it whatsoever, like 0.05 grams of water per cubic meter. That alone is a moisture vacuum. That will at ambient temperature dry out a saturated component. As a matter of fact, faster than the 40C @ 5% process in the 033C spec that many people use. But it’s of course desirable to dry faster. So, every 10°C of heat that you add to that, the time cuts in half. The heat accelerates that drying process. However, we remain at a low temperature. We haven't induced the corrosion that the higher temperatures cause in these alloys. And it becomes a balance and a compromise between how much time do I want to spend on this and how much do I want to protect the solderability? The real kind of eureka moment is recognizing you can do it several times and in a super high-mix, low-volume environment, in and out, back and forth, back and forth off the line. That can be a significant benefit.
Starkey: Which you can't do with repeated high-temperature baking.
Starkey: Because you just thermally degrade the components, you're encouraging intermetallic growth, and you're changing the solderability characteristics.
Heimsch: Even going back 25 years when the 033 standard was first formed, it talks about limiting the high-temperature baking. It is certainly known. To me, it's a recognizable indicator of a change within our domestic U.S. market. Obviously, more and more people are committing to, “Okay, now's the time I get a moisture management process in place.” Lead free, over time, has become a larger and larger percentage of the solder paste that's consumed in the U.S. So then over time they face the same issues and how much better it is to comprehensively manage components.
Because most components do not have unlimited floor life. You can't just leave them lying around. You must have some sort of process control, and that's generating new interest in how this works and what exactly are we talking about. For a manufacturing manager, it might not change his end of line yield significantly. A lot of these assemblies with damaged components pass in-circuit test, pass the functional test and it's out in the field three, four, five months before the failures occur. A lot of the micro cracking will occur on the underside of devices because that's where the encapsulation is the thinnest. It's the water vapor trying to get out and exceed the elastic limit of the encapsulant, and that's the easiest place to escape. You're not going to visibly see that. So, the recognition that it needs to be managed and the baking process refined continues to evolve.
Starkey: The fact that you can effectively build up a database of the drying program you need versus the nature and dimensions of the components that you're storing.
Heimsch: Yes. And the original baking guidelines differentiate between component thicknesses, and the thicker components have a longer floor life because they take longer to reach a dangerous water weight percentage.
Starkey: On the other hand, once they've reached that point, they take longer to pull back.
Heimsch: That's exactly right. Doing the exact same saturating, drying, weighing procedures that were done 25 years ago at 125°C. Components were saturated according to IPC JEDEC specs then put into a 1%, 40°C atmosphere, a 1% 60°C atmosphere, weighed hourly as they dried, and now you had lines to follow for the adsorption rate of the drying.
Starkey: During the drying process, are you drying at ambient pressure or are you drying in a high vacuum or somewhere in between?
Heimsch: No, vacuum was a method used to create a similar kind of acceleration that the low humidity does. Vacuum ovens were used for a long time, and in the early days of the introduction, 10–12 years ago, of these low temperature drying machines, customers compared them to their vacuum ovens. Saturated, weighed, used the same procedures, and found them to be virtually equivalent across a variety of component configurations and tape. There were some occasions where the vacuum oven was a little quicker and some where the dry cabinet was quicker. The other reason that it's really significant is because previously, (and still people do), the only way to salvage overexposed components that are on tape and reel was to take them off the tape and reel, bake them, and then have them re-taped. The tape can't handle more than usually 50°C. But at 50°C and 1% or 0.5% RH, they will dry. Not only is it a better process from oxidation and all that we were talking about before, but it eliminates the time and expense of de-taping, de-reeling, re-taping, re-reeling components.
Starkey: How does the system integrate with your established systems of component storage and component logistics management? Is it fully integrated?
Heimsch: It is. In the automated warehouses, there will be, if chosen, a floor life reset area, and then the rest of it is safe storage below 5%. The system, when it is approaching an expiration time, because time in and out of the safe storage is kept track of, will say, “This one needs to be put into a reset area.” And then when it's ready, the system knows and when it has a spare moment will go get that out and move it.
Starkey: But effectively managing this system, you've got above it an automated management system.
Heimsch: That's right. And if you have a more manual shop, you can do similar things with handheld scanners to keep track of the in and out. The inception of the cabinet was also for the purpose of not having to move components just because they were dried. Because there's no damage occurring by leaving it in there longer than what it needs. Some people choose to do that, depending on their volume and mix; that was the original, "Gee, I need something that I can do both with." And of course requirements, concepts and factory logistics have moved us on into other offerings. We have one that offers two different temperatures at 1% humidity and tracks 20 different batches. So, you can have some at 40°C, the safest of drying temperatures and some at 50° or 55°C maybe because of the tape and reel issue. To me, that's more of an iteration. The real process change was finding something that dropped that temperature. The same way that process change of eliminating nitrogen and yet still not oxidizing was a major threshold in the drying technology.
Another thing that’s always been there but is now growing in need and demand is very long term storage. I mean, years beyond those that the component manufacturers have any handling recommendations for. Military people and automotive people have certainly needed to do this and have for a long time. Because even moisture-barrier bags alone are not good enough for five to 10 years. We've got customers that need to keep things for 20 years. They pretty much understand that the 5% storage environment is a solution. They've also discovered, having done it, that it very well arrests the oxidation, but that intermetallics still grow over time and can render a large percentage of stored devices useless. So, having seen this empirically, we've had customers ask us to add a capability to go below ambient with their long-term storage environment. Because by dropping the temperature you can significantly reduce the intermetallics.
You have to be careful. You can't just freeze it. You can't just keep going low because you got the tin whisker issue. But just like the 60°C/40°C oxidation time compromise, empirically it's been determined by a number of users that 10 to 12°C is a useful yet still safe temperature. So, we had our original insulated enclosures with the 0.5% drying capability with refrigeration to take them down to that temperature. Now, 0.5% relative humidity at 23°C room temperature is 3%, or 4% at 10°C, but it comfortably stays below 5%. There's no more moisture in that environment than there was at the higher temperature, but technically speaking, it's a higher relative humidity. Now, whether that is a problem, nobody's really had the time or the reason to see yet. But you think about it, there's no more moisture, and this is an environment that you're not opening and closing the doors. It's just staying there. So, you're down to a half percent, now you lower the temperature. Yes. You raise the relative humidity. But is relative humidity a suitable measurement for the application? It's not a rhetorical question, but it’s one of those questions that’s out there.
We’ve developed or had developed and utilized quite a different zeolite crystal in our high-temperature 60°C drying cabinets than we do in the ones that are only ambient. It's much more difficult to get down under 1% at 40°C or particularly at 60°C for the recovery time. So, it's a different desiccant in those cabinets. So, who knows, maybe a different desiccant in the lower temperature ones. But to me, the question I haven't had adequately answered is if there are no more water molecules in that environment than there were 10 degrees ago. I agree. It's higher relative humidity, but does it matter? Is that really the guideline?
It's no longer just military and automotive; with shorter product life cycles and component availabilities, more and more people are forced to buy components forward. Especially with the counterfeiting ramifications, you just can't go at the last minute and trust finding a component or finding it and then trusting where it came from. The need to have long-term storage is beginning to spread out to less classic applications. To be able to get electronic parts for a car 20 years old overnight is pretty amazing, but they've been at it for a long time. So that's another demand that’s evolving.
Starkey: Rich, it's been a really fascinating few minutes conversation. I've learned an awful lot from it.
Heimsch: Great. Very nice to see you.
Starkey: I'm sure our readers will enjoy it as well. Many thanks.