designing microstrip power divider for QPA2575 amplifier

Thread Starter

yef smith

Joined Aug 2, 2020
693
Hello, I have QPA2575n amplifier as shown bellow.
I want to build a microstrip power devider and plug them together.
I am used to build microwave systems on a single substrate layers but here i need to design my power divider on a substrate level shown below.
My question is when is what substrate do i use for my microwave power divider design?
What copper thickness should i use ?
Also i incorporate VIA fense form my microwave divider,What layers will my VIA fence go threw?
Thanks.
https://www.qorvo.com/products/p/QPA2575#documents
1690229897887.png
 

ZCochran98

Joined Jul 24, 2018
303
All RF traces (including your divider) I would recommend putting on the top metal layer.

I would also recommend a region on top and around the traces to act as a keepout for the soldermask (in Altium, the soldermask layer is typically a "negative" layer, meaning any shapes you put on that layer are actually where there will be no soldermask in manufacturing - typically, anyway). You want this "keepout" for the soldermask to go on top of the traces, and then for a region around the trace as well (how far away is up to you, but 1-2 trace widths on either side should be fine).

You probably will want your RF GND to be on METAL_2_MID for as much of the board as you physically can assert (just create one massive GND plane on that layer). Bottom doesn't hurt to also be GND (I would actually recommend it, and then connect MID to BOT by a large number of vias around the edge of the board). Power and control routing can also go on the top layer, jumping down to MID when it needs to (but try to minimize the number of power/control lines that pass directly under RF lines; that way, you can avoid discontinuous RF grounding under traces).

As far as metal thicknesses, the stackup already defines the them (2.8 mils for top, 1.7 for mid and bottom).

Your VIA fences will go from TOP to MID. You can have them go from TOP down to BOT as well, if you want. I would actually recommend that; that way it asserts that the GND at MID and BOT are almost the same potential.

Also, make sure, if you can manage it, to get silver immersion, not ENIPIG for you finish, as ENIPIG contains nickel and is more lossy than silver. It'll cost more, but your losses will be decreased. That's an option when you submit your board for construction to the fab.
 
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