Video Transcript – Team PCBFX Presentation

Hello everyone. Thank you for attending our presentation this afternoon. We are team PCBFX and our project is a printed circuit board fixture. Starting off with our problem statement analysis. Our client is Plexus. They’re an electronics assembly manufacturer located here in the Treasure Valley and they were looking to create a printed circuit board fixture with a budget of less than a thousand dollars.

The reason for this fixture is being sought out to augment the assembly process in hopes of reducing board and component damage during the assembly and transportation around Plexus’ factory. Reducing this board and component damage will minimize their financial losses and miss deadlines with their clients. This fixture must be able to adjust to various sizes and shapes, have access to both sides, and handle temperature fluctuations during manufacturing, as well as handle a downward force from the assemblers, as well as the weight of added components themselves.

Then onto our form and function. Our fixture should work with regularly and irregularly shaped PCBs ranging in sizes from 4×4 to 12 by 12 inches. Our fixture needs to survive bake and wash cycles with temperatures around 125 degrees Celsius with zero FOD creation and we’ll get into that more in our testing. We discussed with Plexus that our PCB should hold, I mean our fixture should hold PCBs up to 3.67
millimeters thick. These PCBs should be able to sit in and be securely held throughout the manufacturing and assembly process. Our fixture should have clearance for added components on these PCBs as well as I mentioned needs to handle a downward force from the assembler himself. In the end reduce damage by reducing physical contact from the assemblers with the PCBs themselves. As you can see on the bottom right we have a image of our what our final product would look like and it’s labeled features.

For feature A we have slots for continuous movement of our cross members to adjust to a certain size of PCB so it can fit in.

And then B is the actual shoulder for the PCB to rest on. You can’t really see it that well but anyways the PCB will rest on that and it provides additional support while the PCB is being worked on.

And then for C, these are extended rotary PCB hold downs. The nice part about our design is that in these slots that I mentioned in A we can insert different types of hold downs depending on the situation for whatever type of PCB you are working with.

D is our stainless steel fasteners which are able to handle many iterations of use. And then E is our standoff legs to provide extra clearance for PCB components.

And then in the end if Plexus decides to use our design we hope to have a mass production of two to three thousand fixtures for total implementation across the entire factory.

So the features of our fixture really what make it stand out from those that are already available on the market. Our fixture as Wes said is adjustable to fit various sizes of PCBs ranging from 4×4 12×12 inches. The fixture can be flipped over to allow working access to both sides of the PCB because of our standoff design which also creates clearance for large components on the board. The fixture is lightweight which makes it easier to handle. The fixture is both ESD compliant and resistant to high temperatures which is a rare combination. The fixture will create little to no FOD for an object to breed when it’s used. And lastly our fixture is easy to use we. We use threaded inserts on the slider bars that allow them to be adjusted with just one tool which minimizes the time needed to put a PCB into the fixture.

When sourcing our material we ran into many complications. Because of the PCB bake process the material had to handle sustained high heat of about 125 degree C without melting or deflecting under the load of a large PCB with its components. And the material also had to be ESD safe so it had to have a surface resistivity of less than 10 to the 12th ohms per square. As I mentioned before those two properties don’t usually go together so that was complicated. We also had difficulty finding materials in the proper geometry that were easily machinable and cost effective. So after a great deal of research and contacting vendors we decided to use Durastone and we purchased it from Pentagon EMS.

So we started off by 3d printing a prototype that was a 2/3 scale model of our design. This allowed us to verify the design would work and identify early failures before spending time machining parts. One issue we found was that the cross members didn’t slide very well because the single screw allowed them to rotate too much and bind up.

To fix this problem we changed the screw pattern and used two smaller screws which helped keep the cross members parallel to the outside frame members. We also found that the shoulder depth around the outside of the fixture that we designed for the PCB to rest on was too deep and wouldn’t allow for the hold downs to put enough pressure on the top of the PCB. So to fix this we reduced the depth by about half so that the top of the PCB was flush with the top of the frame member, or sorry was not flush. And we incorporated these changes into our next prototype iteration.

So our next prototype was a full-scale prototype. We used acrylic as our material. Acrylic was super cheap and allowed us to make many iterations without wrecking our whole budget. It wasn’t ESD compliant but we were more focused on how our design was meeting each specification as well as if we needed to make any major changes and see any design flaws right away. It also gave us the opportunity to machine some parts and see our abilities as a team to create a fixture. And then we were able to use this full scale prototype to put some PCBs in there, see if our design can hold irregularly shaped and different thickness PCBs. And we’re able to do a couple drop tests with it to see if there’s any poor design choices and weak points in our fixture. We also found that even using smaller screws on our cross members there to make it easier or to make it less… allow it to rotate less on the cross members. With using two screws on each cross member it was very cumbersome to assemble so we used some threaded inserts later on in other prototypes to help mitigate that and so you don’t need three hands to assemble the whole fixture.

So here’s the drop test of the acrylic. This allowed us to see any weak points in our design and make appropriate changes. We dropped this almost a dozen times. We really mangled it until it was completely broken and it would no longer function at all. In the slow-mo there you can see we are testing it on what we suspected as a weak point being the corners and it did just fine and maintained control of the PCB without allowing it to hit the ground.

Okay so for our third prototype we decided to use Durastone which is ESD compliant and heat resistant. Durastone is a durable and rigid material to handle and which means that it can survive many iterations of manufacturing. The material is generally lightweight to carry which is an important specification in our project. Smaller parts for example the standoffs, the slider that is underneath the the hold downs, and the crossbar link as well as the crossbar itself were stronger than the last prototype. The smaller parts were also machined to improve the fastening of the fixture and its ability to secure any shape or size of PCBs. In this prototype we did decide to use threaded insert as mentioned previously to eliminate the screw and nut tightening system. One issue that did arise when trying to place a PCB on the fixture was that the cross members and their respective sliders weren’t as smooth to adjust but the structural integrity it was strong. Slots in the frame members were adjusted to remove dead spots in the fixture. Overall manufacturing this prototype took a lot of time and patient because we couldn’t use a laser cutter to just cut off the parts of these of the prototype each part had to be machined by hand.

So the next couple of tests on the Durastone are under progress. So we will be doing a drop test similar to that of the acrylic. We’ll do a corner drop, a side drop, a flat drop, and a push-up. So that’s when just an accidental knockoff of the table that can happen anywhere. With this test we’ll identify points of failure and come up with future improvements.

The next test that is still under progress is going to be the bake and wash test. We are trying to assimilate the sanitizing process of Plexus. So we’re trying to see how heat resistant is the material based on its bake or wash. The material itself should handle the temperature that we set to be so 125 degrees c based on the specification sheet. Its operating surface temperature is about 260 degrees Celsius. So we’re just trying to prove that it would work. During the wash cycle or the wash test we’re just going to determine if there is any FOD that comes out of the material. Our hopes and our expectation is that they’re not going to be. But we will figure that out here in a couple of days when we conduct those tests. We will do a couple of iterations of each of these tests just to make sure everything passes.

All right, so one of the tests that we were able to do with our Durastone prototype was for ESD requirements. For a material to be considered electrostatic dissipative it must have a surface resistivity of around 10 to the 6 to 10 to the 12 ohms. Anything higher than this is considered an insulator. So per our our clients requirements it had to be within those those realms there.

So a common way to find the surface resistivity is to use a four point test probe. This works by measuring the resistance between voltage sense two and three while the current is supplied via force on the outer connections one and four. So we created our own four point test probe by 3d printing a holder from PLA plastic and then inserting sharpened welding rods equally spaced to act as the connectors. Those connectors were then attached to a fluke ohm meter and the resistance between the points were found. Luckily we were given information from our sales person of what the composite materials properties should be so before testing we were able to come up with a theoretical value of resistance using formulas provided from Dr. Ackler who is a part of the Material Science Engineering department. However during the actual test we were not able to find this value as we believe the current couldn’t be induced due to it being a fiberglass composite material. So we tried sanding and scratching in several places to avoid hitting the non-conductive glass trans but the values were inconsistent. Some research has found that the industry standard for finding this value is using a device like the Desco Digital Resistance Meter. So currently we’re in the process reaching out to our client to see about using their equipment and if we can’t get a hold of them that’s okay because if the test the spec sheets are correct then it should be ESD safe anyways.

So then for our next plan of action it is to continue to improve upon our design. We would like to do this by ideally putting our fixture into use by Plexus employees and gather feedback as well as test on a wider variety of PCB shapes and sizes. Also we like to ensure that all requirements are met so we want to wash and do several more bake cycles on a long-term plan to make sure that the foreign object debris isn’t created as previous tests were just what the eye can see. So then if this device is to be implemented on a larger scale it would be wise to look into other faster and more precise ways of manufacturing. Because during machining our prototype it was discovered how difficult it was just using the BSU shop tools alone. So an ideal way would be use a water jet cutting device that would reduce the time drastically and make it easier for this prototype to go into mass production. So that being said this concludes our presentation on the PCB fixture for our client Plexus that was meant to assist in the manufacturing process for printed circuit boards.

We will now open the floor to discussions. Is there any questions?

I don’t have any questions. I think that looks great. I’m excited to see your presentation next week. I actually have to drop off for another call but good job guys.

Thanks Aleah. Thank you. Thank you. Yup see you guys next week.

If there’s no questions I guess we just did a great job explaining everything.

A quick question. Do you think if you guys got the manufacturing costs down enough do you think it’ll be competitive with other uh like similar items on the market for these companies?

Yeah, I definitely think so because when we were looking into fixtures on the market I think the cheapest one we saw was what around 500 dollars or something like that? And our total cost of our fixture… What was it Jake you did that cost analysis?

Well it came out to like just under 200 dollars on just material and hardware. And the material because of the properties it has such as the high temperature and the ESD it’s very expensive. So that’s where most of the cost is on the material. But yeah, it is much cheaper than what is out on the market as well as it’s more refined to the needs of Plexus and their environment.

So kind of like a vague comment I guess. I’m not sure if you guys would know this but do you know why like their fixtures were like so much higher in price like if it’s over double them assuming there should be like a reason.

Honestly I’m not sure why. Maybe that’s just the markup for those features. I’m not really sure.

Our price per fixture also didn’t include our man hours or if someone was going to machine it for us so you would add some more price to it. But we did buy the material in a small quantity so you would also save on the material if you were to buy it in much larger quantities just based on bulk price so a little give and take there.

Also manufacturing. If you manufacture more that kind of helps out this stuff because a lot of it goes into the setup price and then you pump out those prototypes for those pieces. But if you’re doing a lot of stuff bulk prices definitely cut down.

Also the idea of our our fixture too is it’s supposed to last or be used for many iterations and so if we were to get these two to three thousand fixtures you know we would hope that they would stick around for a long time. And also the way our project can be taken apart into several different components. If you do have a broken piece, if they’re all machined you know how they would be for water jetting more accurately then you’d be able to just kind of plug and chug if there was a broken component or piece.

Awesome. Well thanks guys. That makes sense.

Thank you. Anything else? All right, well thank you all for coming to our presentation. Have a good day.