Who can make boards with UTQFN package: 0.4mm pitch SMT pads

Community PCB Design
1

I’m working on an adapter for the UTQFN package. This is a 4mm square QFN package with 28 pins. The pins are on 0.4mm centers, with 0.2mm clearance. The board is 2 layers and 1.3 x 1.7" overall.

0.2mm is 7.87 mils, so it looks like this won’t be manufacturable by BatchPCB since their limit is 8 mils trace width and spacing. It seems so close, but I imagine it would be rejected by their DRC.

Has anybody had any experience with any other low-cost PCB manufacturer that can support prototypes with 7mm spacing?

http://www.synthify.com/39477281/684268 … ackage.jpg

2

Both ExpressPCB.com and PCBExpress.com support 6mil traces. I’ve used both companies and both produce high quality boards, but I’ve never had a board made with that thin of a trace.

3

PCB Pool can do 6 mil tracks with double-sided boards.

Leon

4

Wow - the 0.13 mil difference (between 7.85 mil (.2mm) trace width and spacing and 8 mil width and spacing) results in a 10X increase in cost!

If BatchPCB would accept my order, it would cost about $5 US per board.

PCBexpress - minimum $95 US for 2 boards.

ExpressPCB - no bid - allows proprietary software only

PCBpool - Minimum 40 Euro, online calculator give 78 Euro.

I’ll keep looking for more reasonable options and post here if I find anything.

5

You’ll get several boards from PCB Pool, of course.

Leon

6

and how about making the footprint with a 8mil wide pad and a 8mil spacing between?

On the datasheet, the spacing between the center of the first and last pin of a same side is 94.48mil.

With a 8mil pad and 8mil spacing it will become 96mil. A offset of only 1.5mil.

Center the chip and it becomes a offset of 0.75mil on either end. Could you live with that?

7

Olivier,

That is a really good idea! I think for a few prototypes, there would be no issue with that small offset.

I can just create an alternative package on a mil grid rather than the mm grid. Later on, if I ever need to make it a “proper” design, I can just use the other variant of the device.

Does anyone disagree or know of any problems with this approach?