PCB Via Madness - Page 1
Forum section: electronics / general

author: beaker353
author_rank: Unknown
timestamp: January 19, 2014, 08:39:03 pm
content: Pulled open some specialized RF equipment the other day to swap out a bad power supply and found this little beauty. I can't even start to imagine what the cost was to fabricate this board was given how long it probably sat in the drill machine. Full resolution pic of the board is at smokingcircuits.com/pics/via-madness-large.jpg Enjoy!- EM

author: tszaboo
author_rank: Super Contributor
timestamp: January 19, 2014, 08:56:12 pm
content: Someone had fun with the via stiching...I dont think the board would cost that much though. It is usually some 1000 via per 100x100 mm without additional cost, and there are some much denser boards.Can we get high-res closeups?

author: armandas
author_rank: Frequent Contributor
timestamp: January 19, 2014, 08:59:22 pm
content: Wow, looks like a total overkill. They're large vias too, at least 0.5mm I'd guess. What is this equipment?

author: Neilm
author_rank: Super Contributor
timestamp: January 19, 2014, 09:20:11 pm
content: Looking at that my first thought is that there is some sensitive signals buried on the inner layers and all the vias are there to provide screening. You can see the gaps in the via patterns where the signals are running.

author: rexxar
author_rank: Frequent Contributor
timestamp: January 20, 2014, 12:57:56 am
content: Quote from: Neilm on January 19, 2014, 09:20:11 pmBut do you really need a full inch of vias to do that? Surely just two or three rows would to it.

author: SeanB
author_rank: Super Contributor
timestamp: January 20, 2014, 06:39:31 pm
content: Well, they probably did not want to respin the board if it did fail EMC or if it had spurious emissions, so the designer did the via wholesale route. Got really low inductance for sure from top to bottom there. It probably is around 5g lighter as well from losing all the FR$ board as well.

author: beaker353
author_rank: Unknown
timestamp: January 20, 2014, 07:15:02 pm
content: For those curious, the device is a 4 channel RF combiner/power booster for wireless in-ear monitors used in live performances.Background: Many live performers now have ditched the traditional stage monitor wedges speakers in favor of tiny ear-buds connected via a wireless link back to a mixing console off stage. Better isolation from other sounds on stage as well as tighter control over what they hear or don't hear. This device takes the RF output from 4 separate transmit units, boosts each up to 250mW (the legal max in the US), and then combines them to one output that goes to a single antenna (instead of 4 separate antennas). Some of the best sounding systems on the commercial market only natively put out 50mW, so this allows even the weakest transmitter to operate at the full legal power limit. Even for the RF professional sound world, this is a pricy bit...NANDBlog: The full res pic I took located atsmokingcircuits.com/pics/via-madness-large.jpgis the best I have. I pulled the unit to swap out a bad power supply and had to put it back immediately back into the system for show use that night. Uses dual power redundant power supplies for fail-over safety at least so it didn't bring down the show...-EM

author: KJDS
author_rank: Super Contributor
timestamp: January 20, 2014, 08:41:21 pm
content: I think that the via count is one of the least bad things about that circuit.The main RF lines are fatter on the output than the input. It's possible that's because they're playing with low impedances to feed the combiner but I doubt it. There are no vias close to the RF micrstrips, so it gives something more like a grounded coplanar waveguide, but then it carries on off the bottom of the board without the ground plane next to it.The shunt elements of the filtering mostly don't have vias near the grounded end of them, though it's possible that they've used via in pad. Whilst it can be a deliberate ploy to make an LC lowpass have some extra shunt inductance printed with the caps to turn the filter into a quasi elliptic I just don't think that's been done here.

author: tszaboo
author_rank: Super Contributor
timestamp: January 20, 2014, 10:37:07 pm
content: Thank you mister, your effort is much appreciated!Looks like some hackery was going on inside...