Correct way to connect multiple parallel/series MLCC's in a high density design

Thread Starter

SiCEngineer

Joined May 22, 2019
390
Hi,

I have a large capacitance requirement on my rectifiers to achieve a certain voltage ripple, which requires 32 MLCC's. I want to use both sides of the PCB to connect the MLCC's in a more power dense way. What is the correct way to achieve this? The switching frequency of my rectifier is in the 200-500kHz range, which may complicate things. The voltage across the capacitors is also around 400VDC for each MLCC.

Is using multiple vias connected to the sides of the MLCC's and then using tracks to connect them OK? Is there a better way?

Best,
SiC
 

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Irving

Joined Jan 30, 2016
2,669
At lower voltages I'd suggest simply bridging the devices across two power planes; 4-layer boards are pretty cheap these days. But 400v could potentially be problematic at normal 4-layer spacing, so two buss bars appropriately sized and spaced is an approach. Why are you using MLCC rather than SMD electrolytics? 400v close to likely high board temperatures puts a lot of stress on an MLCC which are prone to fracture and shorting.

TDK have a solution to this called CeraLink, which you might find interesting
 

PadMasterson

Joined Jan 19, 2021
36
Having a 400V MLCC must be a larger size for spacing? Your picture is confusing to me in that you have a "Track" that looks like it's running under the parts and not to them? Maybe it's me, (and it IS Friday) but as Irving said, a 4 layer board would work and a typical High Temp FR4 board material can have several hundred volts/mil but you need space between the pads more so. Use the IPC or Saturn calculator to make sure you have the space needed for that voltage. I selected the 301 to 500V voltage and used a Bare board with Soldermask coating and you only need about .0315" of space between the leads. I'm a conservative kind of guy and I would go more for sure, but a 4-layer, .062" thick board should work just fine for thickness, just keep the voltage nodes far enough apart. Also, if you have active devices on that same board, consider the stackup of S-P-P-S as in Top Signals and voltage, center 2 layers, (L2 and L3) as grounds and L4 signals and voltages and don't route on the inner layers if you can help it. Us e plenty of vias to stitch the inner ground layers together too. The typical construction of a 4 layer board will put signals far away from return paths which are a good way to create EMI/noise issues especially if you are pushing some power. Good Luck.
 
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