Respect the PCB
A very belated part three!
My, how time flies! I can hardly believe my last blog post was at the end of August 2013, and now here we are in 2014! Regardless, I want to keep my word and finish up the three-part blog series I set out to complete. So, here I am hat-in-hand, to do just that.
I want to explore what challenges lie ahead for the RF/MW and high performance PCB. Only one problem—I’m only partially qualified to cover this subject! So I thought it would be helpful to end this blog series with a conversation rather than a monologue. So please, be prepared to comment with your thoughts at the end so that others might benefit from your insight or particular area of expertise. I will also invite comments through Linked In, on the RF and Microwave Community and the RF/MW and High Performance PCB design and Fab groups.
RF/MW and High Performance components are enjoying greater speed and performance than ever before. While this is a wonderful benefit to end users, it can be a curse for those of us that manufacture PCBs because we need to do our best to keep up with an imperfect manufacturing process. For instance, etching and plating processes are particularly challenging. If we over or under-etch traces, even slightly, on a high performance PCB your carefully modeled performance can go right out the window. These processes employ chemistry, electricity and a bit of wizardry by keen operators. We work within specified tolerances, of course, because these processes do not yield perfect results. Increasingly I have conversations with engineers asking if we can hold a +/- .001 mil or less on trace width. (I fondly refer to these people as residents of Crazytown!) When a PCB designer is looking at a design on a beautiful large monitor with minute traces that are magnified hundreds of times larger than they are in reality—it is easy to see why these questions may seem reasonable. But when you consider that a .008 mil trace is roughly the thickness a piece of paper you quickly realize that asking for a .004 mil trace +/- a half mil is pretty wild!
Now let’s talk about holes. Similar scenario - whether for space considerations or performance, via holes continue to shrink in size. However, the smaller you drill holes (whether they are drilled mechanically, or with a laser) you need to somehow plate those holes to make solid connections. But, liquid plating chemicals do not like to flow evenly through these tiny holes. More often these small holes notoriously trap air which causes voids. Plugging vias with conductive, or non-conductive epoxy can be a very helpful solution to this issue. But it does add more time and labor which can add some cost and time—neither of which is usually a welcome prospect.
Again, the tolerances continue to shrink and we continually butt our heads against the inherent limitations of the process.
Copper weight and heat
Typical substrate copper cladding is ½ ounce and 1 ounce. You can go well beyond that, but then the etch factor becomes more challenging and holding tolerances is more difficult. However, due to heat buildup of high performance components, additional copper is a perfect solution for heat dissipation. So now folks may want 2 oz. copper with very fine features and tolerances---not a good combo for a PCB manufacturer.
PCB manufacturers and their suppliers continually look for ways to meet the latest demands of the industry—but it is getting extremely challenging as we come up against the very fundamentals of PCB manufacturing itself. So what does the future hold? I am keeping a watchful eye on the developing capabilities of 3-D printing as one potential solution. I’m also keeping my eyes on what substrate manufacturers are continually doing to improve the performance of their substrates. The current challenges make the industry ripe for possible technology breakthroughs.
Now it is your turn
So what are you keeping your eye on? What solutions have you found as you press hard on the performance of the PCBs you are designing? Do you think there is a “magic-bullet” on the horizon? If so, what is it? I am a big believer in collaboration and not constraining ourselves to our area of expertise, or small slice of reality. So, I urge you to comment here and share what you know! We can’t see all things, at all times so I hope that by sharing we can boldly face 2014 with hopeful solutions to the challenges we face. I wish you and yours a happy, healthy and prosperous new year and I look forward to a new year of collaboration ahead.