Wire Bonding vs. Laser Welding with Dr. Mike McKeown, Hesse Mechatronics

Full Transcript:

Introduction

Andrew Thomas: Hey everybody, this is Andrew Thomas at Acculon Energy. And, we’re here with Mike McKeown from Hesse Mechatronics live on day one of the Battery Show. 

And Mike, if you guys don’t know, but, if you know, you know, this is one of the leading experts in joining technologies for batteries or electronic products. And he’s going to spend a little bit of time with us and with you all today talking to us about differences in ultrasonic wire bonding and laser welding. 

And then we’ll have a chance to talk about our own experience as well, working directly with Hesse, on the wire bonding that we do on our own battery modules. So Mike, what’s going on these days In the welding world? 

Resistance Welding versus Laser Welding versus Wire Bonding

Mike McKeown: So every, so it’s about every day or every other day somebody calls me up and says should I do resistance welding, wire bonding or laser welding, and a couple of years ago It was a pretty straightforward answer, they just say, you knew laser you stay with laser welding. Or people knew wire bonding, they stayed with wire bonding. But now it emerges to buy you, to buy you went to laser welding. But that’s not true anymore. A lot of people have stayed with wire bonding, even though their lines have gone up, because wire bonding is so flexible. You have the reworkability, you have the quality monitoring system embedded in the wire bonding, so as you’re making a wire bond, you can tell how well the bond is being made. 

And laser welding systems you have that after-effect. So that’s a separate workstation. And these laser welders are big systems sort of like what you have In some of these booths here. So wire bonding is the size of a big refrigerator. … The other thing that a lot of people haven’t taken advantage of is that the wire buy that can be used in your power modules, your EV trucks, and your e-motorcycles. And for those people in space, you can use the wire binding on the solar panels. So wire bonding is very flexible and for a relatively low cost, say 250,000. You have a lot of machines that can be used in a variety of applications. So it’s not just the battery. It could be an auxiliary item in the EV. 

Application-Specific Methods

Andrew: This would bring up a really interesting point. Mike, in that the joining that you do in the battery has to live in multiple applications.

 I think we get a lot of questions, particularly from space and defense users these days about, maybe it’s just a lack of knowledge about, ultrasonic wire bonding, but, can you talk about what kind of use in very extreme applications, like launching a NEO satellite, for example? 

Mike: Yes. So we deal with that a lot because our customers are very varied. I tell people we’re on drones underwater, and we are up on satellites. So you want … We have the whole gamut. A lot of people, I think, are not educated because they’re not wired bonder engineers. They’re not interconnected engineers. They’re electrical engineers designing a battery For a solar panel for space. So they don’t know the interconnections they need. They may know the theory behind their design, but not practical in the manufacturing or the reliability aspect. And with that as well, for those critical or high-reliability applications, I’ll say to people, you should look at ribbon or multiple wires or working on the design of your battery to optimize, you know, how you get the lowest current, the lowest resistance and to connect, you know, how do you get to, you know, how many amp hours you have to run? So some of our applications only run for 30 seconds you know, very, very, very, very high-powered. So that person is totally different from energy storage which is sitting on a wall of a house, you know, just hanging out and collecting, you know…going to go to work at night. 

Andrew: So, it seems like you and your customers, and the industry, are finding a benefit in the flexibility of wire bonding. But I know you guys do laser as well. Can you talk about what might make a good application or a good product [for laser welding]? 

Wire Bonding Flexibility versus Laser Welding Durability

Mike: To be laser welded It all comes down to the base metals, you know, assuming in wire bonding and then in small welding, you need a good base metal system and it really depends on the application, you know, are you going to do high volume 24/7 production and you can’t have this unit/this device fail? You know, you don’t want to be stuck on the Long Island Expressway because you know, your wire bond messed up. So, it used to be a higher volume with the laser, but that’s not always the case. But the laser is not a fusible link. So if you’re going to go into space and that interconnect has to last ten years, maybe laser welding might be better. Okay? It depends, again, on the application. 

Andrew: I think I’m going to bring in Karl who does a lot of the wire bonding on modules for our products and the customers that we work for. And I’ll let you guys talk a little bit about what you’ve learned as we’ve gotten gotten started and got a lot of experience in the last two years in wire bonding to a variety of different types of cells and materials using different, types of wire as examples, like hard, soft, medium diameter, and the types of ribbons. So, Karl, you and Mike talk about our 48V module. 

Karl Moghissi: Yes, I’m happy to … This is the module we’ve been working on, and we’ve obviously settled on the four wires, for the same reason you mentioned: opting for reliability. And I have really appreciated the flexibility of using the wire bonder, and that we have changed our design in terms of PCB multiple times. As we’ve made those changes, we have been able to very quickly adapt to that change by basically adjusting the program, especially with the way that program has been laid out, and are able to find very few wires and need to have that expressed cost that has been a bit appreciating … 

Acculon’s Wire Bonding Experience and Mike’s Bonding Advice

Karl: So Mike when you look at the way we’re doing the wire on our module what would be some of the comments that you would share with us? 

Mike: Two of the most common challenges, I would say in wire bonding is the fixturing of how you mount this battery onto the wire bonder and then the cleanliness. And there’s also how you lay out the circuit board structure, and how the cells are situated in the matrix. So those are key items. You can’t have any movement with the wire, any movement that will cause a translation later on for movement of the wire–they’ll sever at the heel. So, you know, you have to really have a good solid design. 

We have 3D models of our bond heads that you can incorporate into your CAD to make sure you have sufficient clearance because we front-cut bond heads and back-cut bond heads. So we have those tools. but normally you could tell about how “neat,” you know, or clean the design is you can tell if this is a wire-bond ready, you know, battery pack just by looking at the nice clean surfaces. You don’t see any movement of the cells. So it’s … those are the main challenges when wire bonding. … 

Bonding Evaluation for Reliability

Karl: So looking at this, what would you look at in terms of future changes that would be something that would make sense for specifically this module and the application that will be using it?

Mike: So right now I don’t see any, you know, “red flags” coming out. With wire bonding, we can look at the bond waveforms to see how the ultrasonics/the bond deformation–how those are characterized and maybe tweak some of the parameters because not all the wire is on the same. Okay? Bonding on a positive terminal and bonding on a negative, you can have different parameters. I mean similar. However, it could be slightly different based on the bond waveforms. So that’s one of the things we suggest to people. Once you feel comfortable with your pull test, sheer test, and visual. Then take a look at the waveforms and see where else you could improve on. So, right now, cosmetically, this looks great. 

Karl: So as we start looking more into production, where would you look to see in terms of a per cell or per wire basis in terms of how reliable that quality is… Like, how many failures would you expect to have out of a thousand? 

Mike: We hope to have none. But ideally, we tend to have problems when there’s contamination. Or fixturing [problems]. If those two [problems] are not present, you should be able to wire bond 24/7. It’s that simple. The wire bonder doesn’t know that the next part coming in has, you know, contamination on it. It’s going to bond but it may not stick. 

So that’s our job as wire bonder engineers to not just work at the wire bonder but work further upstream to make sure that the adhesive dispenser is not putting out too much adhesive and causing some overflow that’s going to affect pattern recognition, things like that. So a lot of times the problems are found at the wire bonder but they’re not from the wire bonder. They’re from further upstream. 

Andrew: Awesome. Well, Mike, and Karl, thanks. Thank you for your comments and your insight And everybody have a great week here in Detroit at the Battery Show!