Blind & buried vias

[wattbrew]

Do any members have experience with BBV technology? Is it really a viable way to shrink a board and save any considerable weight? My company wants me to investigate routing manually using blind & buried vias to see if we can shrink the boards down to cut weight. I am skeptical that I will save enough space to justify the increased cost. If anyone with any experience in the area can offer tips or advice, I would be appreciative.

Thanks,
Bill Watt
Moog inc
716.687.5596
wwatt@moog.com[EMAIL]

[phillipr]

Bill

I'll Need a little more input to answer your question.

How many layers are you looking at?
What kind of profile Pcb size?
Component technology (Bgas,Qfps)?

[wattbrew]

Phillip,
I am trying to determine if BBV technology will help me shrink a board size to any extent. Our typical board will be approx 3 x 4 inches and contain 8 layers, 4 routing and 4 planes. We are currently using fpga's in qfp packages along with many discretes and other small chips. Is this routing technique going to decrease the board area or only the layer count?

Bill

[Colorado-PC-Dude]

Bill,

I think any time you can remove something from your component placement area (top or bottom side) you stand to gain area. The question is if you'll gain enough. I've had limited experience with blind/buried vias but for us they saved some space and made the board smaller. I think you'll just have to give it a try and determine if it works for you.

Ben

[JimR-OCDS]

I did a blind and buried via board just recently. Luckily I was able to have the board built in China, because the cost increase for a blind and buried board in the US, is huge!

[Tom]

I have discovered that if you use Blind & Buried vias that you should use a lot of them. Once you enter that technology the cost goes up even if you only have 100 of them. The cost for 1,000 of them doesn't increase very much and the cost for 2,000 doesn't increase very much either.

Some designers who have to use Blind Via technology to solve a 0.65mm pitch or 0.5mm BGA get burned if they only use the Blind Via technique for just the BGA. You might as well place your GND planes near the outer layers and Laser In Pad all the SMT GND connections. I recommend several GND vias per SMT Pad. The manufacturer will plate them and then add a surface finish (like Gold or Silver) and you can't even see the blind vias in the pad. Engineers like this technique because it increases capacitance and reduces inductance.

The following illustration shows the definition of various vias in a constructive manner. It compares a standard through-hole via, standard buried via, controlled depth drill via, and various other conditions. A few unusual techniques are the trepaned via (#8) which traverses several layers, mostly used in HDI production, or the reverse blind via which has added to it a via cap that is intended as a test point and therefore needs a conductive surface in order to provide access.