RF and Microwave PCB Design with John Bushie from ASC

What material do I use? Many PCB designers ask this question. This is an episode about RF and Microwave PCB Design as well as Design for Manufacturing or DFM and it will help you to understand material choices and where to get answers about high speed laminates. Join John Bushie, Director of Technology at American Standard Circuits and Altium's Judy Warner in a discussion about High Speed laminates and the exciting world of RF/Microwave PCBs.

 

Show Highlights:

• John and Anaya's new book on iConnect007 about RF/Microwave PCBs
• You can design something that meets IPC standards and still have problems.
• What kind of material do you need? That depends.
• There's what you simulate, and then there's physics. Physics trumps theory.
• PCB101, a manufacturing educational experience pioneered at ASC

 

Links and Resources:

• American Standard Circuits website
• The Printed Circuit Designer's Guide to Fundamentals of RF/Microwave PCBs
• The Printed Circuit Designer's Guide to Flex and Rigid-Flex Fundamentals
• John Bushie on Linkedin

Hi everyone, this is Judy Warner with the OnTrack Podcast, welcome back. Today we have a really great guest for you. I'm really looking forward to sharing my guests with you and please, if you would follow me on LinkedIn or on my Twitter which is @AltiumJudy and if you would like to follow Altium you can go to our Facebook, Twitter or LinkedIn profiles.

So let's get started. Today I have the great pleasure of being with John Bushie who is the Director of Technology for American Standard Circuits which is outside of Chicago area and ASE specializes in both RF microwave circuits and also flexible circus but today I want to talk to John about a new micro Ebook that they have published through iConnect007 and this book is near and dear to me.

Some years ago I wrote a guest blog on a microwave journal because so many RF and microwave engineers and just engineers in general are being tasked with designing their own boards. And particularly in the RF and microwave space a lot of these designers, these guys are designing boards and haven't had the opportunity to spend a lot of time in a fab shop.

Yeah, and they really just don't get a chance to be exposed to as much as we do being a fabricator. Since a lot of the people at our organization tend to be a little bit grayer in appearance we all have a lot of experience and the reality is is we can share this with them. One of our most important jobs is being able to educate them, and that's really how I think of myself, educating other people sharing the knowledge that I've gained over the years and just trying to help them out with their designs because ultimately we just both want to be successful.

Yeah absolutely and as you know, I spent 25 years or so in the fabrication industry and when I had a stint in the RF and microwave industry and it was like culture shock, John, like it just felt like a whole different animal, it was like drinking from the fire,

Were you working with the designers at that time?

Yeah so it was like... and I felt completely inept at first when I started there to talk about laminates but all of a sudden we're talking about performance instead of just mechanical dimensioning and making…

- sure we're just used to meeting specifications right?

Right!

- And those have a physical dimension to them and the route is you start getting into this realm of higher frequencies and you start to find out what's really important to these designers.

Yeah, and I started to feel it, the more and more I learned the more kind of stupid I felt and the more I realized; holy cow there are so many ways that a board shop could screw up and there's literally…

There’s literally thousands of different ways we could manufacture the same board and the reality is is we always have to try to manage any of the risks that the design presents and certain aspects of certain designs actually will will present problems, or they'll complicate other features that are important to the RF designer’s ultimate performance goals, and so working around those issues is what is so exciting about it.

It is exciting.

It's really challenging and fun and what was really stunning to me is to really get to the point where I realized; oh my gosh we could be 100% compliant to IPC standards...

-and still have something that doesn't work...

… and make a trash board - that's exactly correct.

Because you know we’re within tolerances so we did a little of that, but you know what, if we over etched and you know that circuit had a little too much under or over etch or whatever that the performance went to heck and and they're like, no this is not what we simulated in and we're like, too bad so sad it's the IPC standards so it's a lot more complicated. So why don't you go ahead and talk about, sort of this is now? This is a book I wish I had enough brains to write so I'm glad you did.

Don't give me too much credit.

So why don't you tell us a little bit about it? Well first why this book?

I just wanted to share the knowledge that I've gained and I've had the opportunity and the great fortune to be able to work at several world-class fabricators. Poly Circuits in my early days helped get Mega Circuits into PTFE materials and now with American Standard circuits. But in the middle there - I was also able to work for an RF circuit board laminate company at Taconic. Well I got to work very intimately with the designers in North America as well as Asia and Europe so it's the ability to be able to interface with what are some of the most brilliant people I've ever met just taught me so much and when you talk about coming into something feeling completely ignorant… well that was me a long time ago and the reality is now I I hope that I can share some of the knowledge that I've gained through all this experience.

So since I know you've been it Taconic you probably told me that before, and just wasn't remembering it. But let's just pause there for a second and just talk about composition of high speed materials.

Sure.

Because that was kind of the first place I started and the realization of you know with Upper 4 you've got some fiberglass resin…

- resin, glass, maybe fillers and there you go and you're off to the races. Now talk about high speed materials, the different compositions what, they are?

What they are and… traditionally high-frequency materials were generally all PTFE based and what that meant in the early days is that there was very few flavors I think everybody knows the term Duroid. great materials fantastic from an electrical performance standpoint. But some of the mechanical properties were perhaps a little lacking and that's really the largest improvement we've seen in materials throughout the years.

It’s the increase in strength and dimensional stability of these materials which makes it easier for us to fabricate because honestly if a material moves around a lot during the physical stresses that we put it through then we have tendencies to have registration issues, or it causes other issues within our manufacturing. The biggest change in the materials nowadays is the change to higher thermal conductivity materials. That's where we see the market going and respect to those types of products as the power levels go up and designs get small. Everybody's got to deal with these heat issues that they've got.

And I'm sure automotive is driving a lot of that.

Well automotive does too... that's an interesting… another realm that we're talking about, is these very high temperature materials and a lot of the underhood automotive application. It's something we just get a little bit of exposure to but it's also a very interesting field.

Yeah just one of the things you mentioned too are... I neglected to mention to our listeners that we are here at Design Con in Santa Clara, so if you hear some voices in the background it's because we're here at a trade show and so just wanted to mention that so ASC is here with a booth and also rolling out hard copies of their book so. So the going back to the laminate side. So, I know from the RF experience I've had that each of these compositions of materials behave differently right?

Mm-hmm.

Like when I think of PTFE distinctly and there's a completely different system, you know?

Distinctly, and when you go from the the thermoplastics to the thermoset materials both have their advantages you know. PTFE is a fantastic material in that it's largely inert. It's inert to the effects of high frequency radiation and it doesn't change and that's what yields the fairly consistent results that you get with PTFE materials.

Now there's the introduction of the lower-cost thermosetting materials that also have pretty good electrical properties and that that can be a huge benefit just in the rigidity. Overall dimensional stability and the fairly low CTE values you know. At the same time, they've been filling PTFE materials for years in order to alter their properties and they've actually done a phenomenal job and bringing the CTE values very close to those of copper, which is the ideal since every board, every layer is clad with some level of coppers.

Right.

Yeah I mean we could devote…

You know I this is an interesting subject and there's a new material that comes out virtually every couple months all right and there's just a lot of good materials out there there it really is which is really what the whole key to this.

Yeah which is really actually good for industry great for designers right?

Which is why when we get asked the first question that everybody asks is what's the right material for my design. That's an impossible question to answer on the face of it but the reality is, as we dig deeper and deeper into these designs, we can kind of get a sense of where their price sensitivity lies, what level of performance they need, and just just seeking to go through the process and understand what their requirements are.

Before we got down that road... if I read - I had the pleasure of reviewing your book before it got published - and don't if I remember correctly. Don't you have a chart there or is it on your website that shows, like side by side, all the differences?

We do, it compares all of the various laminates that we use and actually, I had had a ex-colleague from that company that I used to work for mention that.. hey I left out a few of the most recent materials particularly in Europe. I apologize Manfred, I did not know that there were materials released, but thank you for catching that and I appreciate your insights. Because you know again going back to that subject. I've been phenomenally lucky to have worked with some fantastic minds as well as fantastic people in this.

Which I'm sure is an awesome asset for you at ASC. So okay so give us a quick rundown again. This is a micro book this is not a textbook?

Yeah and it was never intended to be a treatise on the subject it's really to touch on some of the major - I'm gonna call them issues for lack of a better word - because if we don't deal with them at the beginning of the design they can end up taking what is otherwise a fantastic board and make it virtually non manufacturable and this is really about DFM.

It really is.

You know we go into all the subjects - obviously not every subject as it relates to circuit boards - but from material selection, to copper roughness, to choosing the right stack ups and balancing your constructions whenever possible. How does copper thickness play a role in the ability to be able to manufacture? To find fine lines and spaces, edge plating, cavity constructions, thermal management. It touches on that wide variety of subjects and it just kind of gives you an overview of what we deal with. What to be thinking about when you're going through this process and hopefully it'll be an aid.

Yeah well,  I can imagine that this will be a great sort of starting place because I'm sure you get asked these same questions over and over again?

Yes and the reality is, is we want it to start the dialogue right you know - and we want to be able to put something in your hands that can aid you right now. But also help you think about certain aspects so that we can work together right. We've dealt with some designs that deal with basically a composition of every circuit technology known to man in one board but since we've worked so in-depth with this customer for a very long period of time we've ended up balancing out the performance requirements that they need with our ability to be able to manufacture right. Because it doesn't matter whether it's the highest performing smallest assembly in the world, if we can't make it or we get 10% yields, it's it's not going to end up satisfying the customer.

Yeah and that's another thing I remember feeling kind of pounding my head against a wall like you know now that I'm on the EDA side of the market right, there's such good powerful EDA tools out there and, but they won't necessarily flag you and say, no dummy you can't...

Yes indeed you're right, and that's exactly what ends up happening. I mean we've gone through designs where people expect to get a certain level of performance and all the materials are there, the components are there and we find that one aspect was missed and you know, there could be copper roughness. Oh we didn't account for that right. So you know we get, hey I'm getting minus 3db down from what I expect to be getting that's a huge loss it’s almost double.

Yes so there's what you model and then there’s reality.

My friend used to say, there's what you simulate and then there's physics.

Exactly then there's, yeah physics gets in the way right? And then John Toussaint who actually works for you guys, his favorite line used to, be physics trumps theory.

Right very true.

Right? So you know there's just limitations to what we can manufacture so well this is a really, really great again as I said I wish I had the ability to be the one that wrote this but I'm so delighted. I think it's truly a great service not only to your customers but just to the industry to get this information out because it's sorely needed and to my ability no one has really put this out you know...

No I'll be very honest if an a hadn't worked so hard on this project it never would have been realized either so thank you for pushing on this project and driving it forward I do think it will be helpful to great many people and who knows, maybe there'll be some addition to this in the future.

Yeah that would be great and I know you guys have written one actually which maybe is another Podcast series we can talk about…

The rigid flax which is that is becoming more and more.

We're actually seeing the two integrated in some instances. Yeah when I was referring to that one design that's exactly what we're talking about. Yeah IMS flex RF FR4, multilayer blind and buried vias and flex later. Right and the middle core I'm sorry I left that out.

Oh good lord... but manufacturable - piece of cake! Can’t you give me. you know $10 off that board John?

Sure exactly we're gonna deal on price, but you know, you do what you can there and you know you've got to try to make it. You've got to try to make it successfully and usually we try to make it for a cost.

Of course like people, not everyone really understands. I wish I could take every designer and engineer and they would be like forced to go through board shops like five times.

You're right. I mean we even created a tool for that called PCB 101 just to kind of give you a good overview. Once you start breaking it down and you think of the circuit board processing as each path is in itself a process right. Then you start to add up all the processes that the board is exposed to as it goes to the manufacturing operation. When we get to some of these complex designs it might be going through 150 - 200 different operations.

Yeah, exactly right.

And all of them have potential risks so absolutely...

Yeah people don't really… you know, we've come to sort of take for granted printed circuit board manufacturing. I think we're all impressed with semiconductors and their performance and bla bla bla - boards are… they're dumb and they’re just boards and they just lay there or whatever.. except unless that that board is made right none of those parts work.

And with high-speed digital ou have controlled impedance with RF its dielectric constant line width and loss. So I mean you've got one or the other.

Yeah and now with the added dimension of thermal management, since people are becoming a much more... which is fantastic because it can offer performance levels that weren't even theoretically possible just you know five ten fifteen years ago you know.

So let's talk about where people can find the book first which I think is on the iConnect007 website correct?

That's correct.

And and then where can people find more information about ASC John?

They can go  to www.asc-i.com.

Okay let me check that one more time - www dot ASC (that’s American Standard Circuits) dash-i dot com - okay very good.

So is there anything else that I may have not covered or asked you relative to this awesome book you just put out?

No it's just all I do, is just encourage people to give it a read, say that it's downloadable for free.

Yes it doesn’t get less expensive right?

It doesn't get less expensive.

So you basically just put in your name and your email and download it and it’s a PDF right? So it's a digital ebook.

I'm gonna look over just to get a little bit of agreement, that is in PDF form is that correct?

Yes it’s in PDF form.

Excellent okay PDF form and, here at Design Con you guys have brought a limited number of hard copies to give away so I'm sure those will be appreciated and and I'm sure once you start getting readers you'll probably end up printing out more of those but, well thanks so much for your time okay.

So now for the fun stuff I'm going to ask you two fun questions. First what is your favorite techie gadget that you own?

Wow that's difficult…

Like that you can't live without...

Well I mean everybody's gonna say their smartphone nowadays but besides that, yeah I'll be honest, no I always go back to home entertainment. I'm sorry okay.

Well hey that is totally okay. Do you have like a pimped-out home entertainment?

I have a pimped-out setup at home.

Okay let's hear it let's hear the specs!

It's got over a horsepower of wattage, it’s considerable it's got 13 speakers. It's a little excessive - nuts. People say I’m nuts when they go into my house but that's alright.

Is it like a home theater.. little home... wait how big is your screen?

It's only 60 inches I'm trying trying to talk five feet I'm trying to talk the wife into the 80 inch OLED but for some reason that thirteen thousand dollar price tag is a little steep. So we're gonna wait for the price point to go down.

My second question is… I know you're not a printed circuit board designer but a lot of us techie people have kind of interesting creative hobbies and things.

I'll be honest I'm the exception to that. No I shouldn't say that actually... actually I've been a bit of a computer nerd always have been, uh used to spend way too much time on computers. I think I set my first network up at home to be able to online game with, or at least network game with buddies back in 93.

So you're dating yourself?

Yes I am.

I was there.

Right but I know you can't stop getting older Judy, so...

That's right.

Okay I decided I'm gonna start counting backwards on my birthdays, that's how I'm solving that.

Okay so anything else or shall we wrap up here? Is there anything else you wanted to share that I might have left out John?

I think we pretty much covered everything Judy, appreciate the opportunity.

Oh and is there anything of note that you guys, other than booths and talking to a whole bunch of people for a couple days. Is there anything else that you guys are bringing besides your book to this show that may be of interest to or listeners?

I don't have any specifics that come to mind. I mean the reality is this is what we're working on right now. We're bringing this effort forward and hopefully, like I said, people will find value in that but the nice thing is there's our rigid flex expert Dave Lackey and myself so when we come here we try to bring some value to the people that might stop by

Okay so while I have you recorded on it, will you promise to say... send Dave Lackey back to talk to us about rigid flex?

Well we will round them up and send them in here okay?

Great tie them up okay!

Great well John thank you so much and thank you again for taking the time and effort to put this book out. I think it's going to be of great value to the industry for certain. Your customers and I really appreciate that laminate chart you put together - I wish I had that a long time ago.

Exactly.

Well thank you very much and have a great show.

Thank you again this has been Judy Warner with the OnTrack Podcast please remember to subscribe and add us to your favorite RSS feeds and we look forward to talking to you next time and always stay OnTrack.