nRF 52840 PCB design

[Maksim]

I am designing a pcb just the nRF 52840 MCU. The design of the PCB is based on the reference design from Nordic. 
When ordering the PCB I came across a problem that the vias under the MCU are too small and too close together to be able to order the PCB for a 
normal price. 
I have been informed that the technique with which this can be done properly is a laser technique that companies like Eurocircuits.com do not have. 
This means that I cannot realize the design before this problem can be solved. The chip is constructed in such a way that the vias must be so small. 
Is there an alternative where I can order the PCB for a normal price or are there cheaper design options that reduce the costs?

[Andreas]

Hi,

 

If you do not use all the GPIOs you do not need vias for the pins that are not in use. If using a few of the innermost pins you could try to use larger vias, but you should then submit your design here for a review (you may open a private ticket so it is not publicly visible).

I have also seen examples where the innermost pins have been routed out between the outermost pins, but this is also something that probably comes at a cost. Unfortunately it is hard to get the best of bothworlds, and not expect having to pay extra for it.

 

Using many large and through vias breaks up and degrades the grounding of the IC. There are sensitive modules onboard that require good grounding to operate properly.

 

Also see this application note: https://infocenter.nordicsemi.com/topic/nan_040/APP/nan_040/nan40_intro.html?cp=11_0

 

Best regards,

Andreas

[awneil]

Have you considered using a module?

[wpaul]

awneil said:

Have you considered using a module?

I was going to suggest this too, but this depends on two things:

1) Will a module physically fit the desired PCB design (I know some people want to build really tiny boards)

2) Will the added cost be a problem

You can buy the nRF52840 IC in large quantities for about $4 each, but for the Rigado BMD-340 it's more like $8. However with the BMD-340 you also get a built-in BLE antenna and an integrated 32MHz crystal. Whether that balances things out or not depends on the application design, I guess.

My friend and I elected to go with the Rigado module for our project primarily to avoid (we hope) potential problems with the nRF52840 footprint. We were able to do a large order to help reduce the per-unit cost. It was still annoying to route everything, but not as bad as it might have been with the IC itself.

-Bill

[awneil]

Yes, the per-unit cost of a module is higher.

But the design cost of getting a PCB right and fully qualified is extremely high; as the OP has found, it is not a trivial exercise - and that's before even getting onto the RF parts!

It's generally reckoned that a a bare-chip design is unlikely to be viable unless you're looking at volumes over many tens of thousands.

https://www.silabs.com/whitepapers/six-hidden-costs-in-a-99-cent-wireless-soc

https://devzone.nordicsemi.com/f/nordic-q-a/48284/nrf52832-wlcsp-ciaa-rf-do-not-work/191537#191537

https://devzone.nordicsemi.com/f/nordic-q-a/48816/regarding-the-schematics-of-the-nrf52/193876#193876