Small PCB using JLCPCB SMT process

Thread Starter

Kaisha

Joined Nov 23, 2016
15
Bit of a beginner here, I've created two PCBs using easyeda + JLCPCB with their SMT process. Both have worked great. I'm working on a 3rd design but its smaller than their SMT process supports. To that end I've made a larger board with cutouts/tabs:

PCB_PCB_2020-05-05_17-14-05_2020-05-08_10-58-41.png

The grey parts are the cut out. The entire board size is 43x26mm, the inner board is 33x16mm. The 4 cutouts are 2mm wide and the corner tabs are ~2.8mm thick. Do you think this will print/assemble correctly? Do I need anything special to cleanly cut the inner PCB out of the frame? Should I do something completely different?

I've posted a similar thread in the easyeda/JLCPCB forums, but so far it's been quiet. Any thoughts/ideas appreciated.
 

jpanhalt

Joined Jan 18, 2008
9,426
Does it work?
The pictures are very pretty.
Your traces seem to be unnecessarily thin.
The via-thermals (?) under the large chip (an MCU?) are a lot fewer than one usually sees. But since there are no dimensions, who knows?
Do you have a question that can be answered?
 

Thread Starter

Kaisha

Joined Nov 23, 2016
15
I think it'll work, its very similar to the 2 other ones I made with the same chip (an esp32-pico-D4) and both worked great.

The traces are 10mil for signals, and 20mil for power with a ground plane and power plane handling most of power distribution (its my first 4-layer design).

The MCU is 7mmx7mm, the whole image is scaled up 2.5x for visibility. I can post a pdf if that would be preferable. The bottom pad is a ground plane, and from my understanding thermals aren't an issue on this chip. Again, on a near identical design I've had no thermal issues. Though I could put more if you think that would be advantageous. I read somewhere that too many via's under pads can cause issues with solder flow, so 5 was just a guess on my part.

My concerns were mainly with the cutouts (the grey sections); the idea being, that I can cut-out the inner board away from the outer frame. I don't know if there's any special considerations that need to be made for large cutouts like that. How thick should I make the 4 'tabs' that connect the outer frame to the inner (currently they are 2.8mm). Any special considerations when cutting the board or just use a good pair of scissors?
 

jpanhalt

Joined Jan 18, 2008
9,426
How cutouts, slots,etc. are handled depend on the CAM processor used. What Gerber CAM processor are you using and what layers are involved? You need to download one of the many Gerber viewers and see whether what will be made is what you want to be made. Your board maker can help. I got no help from JLCPCB with respect to slots, despite sending it Gerbers and PCB (Eagle) files. Just FYI.
 

jpanhalt

Joined Jan 18, 2008
9,426
Exactly as I said. Eagle doesn't support slots the way many other programs do. I submitted my question to JLCPCB as to whether what I drew would result in a plated slot.* After several go arounds, I sent it everything I had, that is, screen prints, .pcb file, and Gerbers created with the EAGLE cam. No response after 6 weeks and counting.

Your board is not a simple board. It includes cutouts. Be sure your board supply house will give what you want. Of course, the price seems very cheap at some houses, but
how much is your time worth for redoes?

*As legend has it, all you need for a plated slot is copper on both sides. Try it, and see if that works for you. How are a drill, hole, and milled slot treated? Does the slot (etc.) need to be connected to a signal? If you don't care about plating, then the matter become much simpler.
 

n1ist

Joined Mar 8, 2009
184
Slots are milled with a router bit; for JLCPCB the minimum slot size is 0.65mm. They won't be able to make the sharp trapezoidal ends you are asking. Cleanly cutting the PCB free will also be a problem. I would panelize the design (or have them do it) using either v-score or routed with mouse bites in the tabs. I would place the tabs in the middle of the long edges, not at the corner, to make it easier to snap them.

In addition, you DO NOT want those traces and pads near the antenna; it will mess with the impedance and performance.
/mike
 

Thread Starter

Kaisha

Joined Nov 23, 2016
15
They don't support v-score or automated panelizing with their SMT process.

What are mouse bites? And how far away should traces/pads be from the antenna to prevent issues?
 

nsaspook

Joined Aug 27, 2009
7,298
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