i.MX ProcessorsのトピックRe: i.MX8M Plus PCB Design

i.MX8M Plus PCB Design

Wobaffet — Wed, 05 Oct 2022 05:59:48 GMT

Hello,

In our application we would like to use the reference design for i.MX8M Plus. The evaluation kit has two PCB's. One is a compute module and the other one is base board. For our design, we would like to merge them into a single PCB but the PCB thickness for compute module (CPU) 1.2mm, the other one is 1.6mm. What is your suggestion in our case? Thank you in advance.

Re: i.MX8M Plus PCB Design

Manuel_Salas — Wed, 05 Oct 2022 17:17:29 GMT

Hello!

You can refer to the Hardware Developer’s Guide (table 14, PCB recommendations)

The Hardware Developer’s Guide recommendations apply to a board of any size. There is not a defined rule for PCB thickness.

Best regards @Wobaffet !

Re: i.MX8M Plus PCB Design

Wobaffet — Thu, 06 Oct 2022 06:17:46 GMT

I've read the document. I'd like to copy CPU board layout into my custom board. But the thickness for CPU board is 1.2mm and our custom board is 1.6mm.

In our case would the impedances change?

Do we need to modify the layout?

Re: i.MX8M Plus PCB Design

Wobaffet — Thu, 06 Oct 2022 06:42:05 GMT

I'd like to copy CPU board layout into my custom board. But the thickness for CPU board is 1.2mm and our custom board is 1.6mm.

In our case would the impedances change?

Do we need to modify the layout?

Re: i.MX8M Plus PCB Design

Manuel_Salas — Thu, 06 Oct 2022 13:20:54 GMT

No problem, the impedance is affected but in a "good way" decreasing, and a little more of heat dissipation.

Best regards @Wobaffet !

Re: i.MX8M Plus PCB Design

Wobaffet — Thu, 06 Oct 2022 14:23:21 GMT

If so is only delay matching of traces important for LPDDR4 and eMMC? Isn't there a trace impedance requirement for these signals?
Should the material of the PCB (TU768) be same as the NXP evaluation kit?
For other signals (LVDS, Ethernet etc.) should be impedance controlled? Is this correct?

Re: i.MX8M Plus PCB Design

Manuel_Salas — Thu, 06 Oct 2022 14:33:26 GMT

The LPDDR4 impedance is controlled for the PHY. So, remember when you have your first custom board you will do the DDR test for be sure that is working.
Yes, the material TU768 should be the same.
And yes, you are right, the impedance should be controlled.

Re: i.MX8M Plus PCB Design

Wobaffet — Fri, 07 Oct 2022 14:21:41 GMT

There are different packages for RAM as following. I think the difference between them is thickness of the device and ball path diameter (Ø). Can we use these packages in the same layout because depending on the capacity of the RAM, package code changes. We would like to have different variants for the same PCB.

Package Codes
DS = 200-ball WFBGA 10 x 14.5 x 0.8mm (Ø0.35 SMD)
DT = 200-ball VFBGA 10 x 14.5 x 0.95mm (Ø0.35 SMD)
NP = 200-ball WFBGA 10 x 14.5 x 0.8mm (Ø0.28 SMD)
NQ = 200-ball VFBGA 10 x 14.5 x 0.95mm (Ø0.28 SMD)

Re: i.MX8M Plus PCB Design

Manuel_Salas — Fri, 07 Oct 2022 17:30:08 GMT

I could not any documentation of the Path thickness, for IMX8MP is used the "DT = 200-ball VFBGA 10 x 14.5 x 0.95mm (Ø0.35 SMD)".

Any way, the changes are not significant, in all case, the most critical case is the "NP = 200-ball WFBGA 10 x 14.5 x 0.8mm (Ø0.28 SMD) ", but as I said, the changes are a little insignificants.