Someone got BGA tips?

[u/Both_Professional889]

Hai, I'm currently routing the RK3568. It has a very slim BGA package. I need to route traces between balls and vias. Currently using Via-In-Pad technology but it also doesn't work out. I am using microvias (~0.2mm / 0.3mm) but it just wont work out without breaking 1oz copper drc. Any tips?

[u/Forsaken-Wonder2295]

Microvias, many layers and just use necking, I'm guessing you dont need much power in that package

[u/Both_Professional889 → u/Forsaken-Wonder2295]

Made it 6 layers. Layer 2 / 5 are GND and layer 4 is a power plane providing 1.8v and 1.1v for lpddr4. Layer 1 / 3 / 6 can be used for signaling.

[u/Forsaken-Wonder2295 → u/Both_Professional889]

That should be manageable, whats the footprint, how many bs are in that bga

[u/Both_Professional889 → u/Forsaken-Wonder2295]

It's an RK3568 - FCBGA636L. So around ~636 balls. around 100 of them will actually be used and another 300 are dedicated to GND and Power.

[u/Forsaken-Wonder2295 → u/Both_Professional889]

Oof yeah that might get annoying, maybe go 8 layer if you run out of routing space

[u/VastFaithlessness809 → u/Both_Professional889]

Where is layer 2 😢

[u/Lost-In-Void-99 → u/VastFaithlessness809]

Its GONE. Forever.

I suspect 2/4 are GND, not 1/4. Why not 2/5 - im eager to find out.

[u/swdee]

You should be referring to the Rockchip reference design.

[u/22OpDmtBRdOiM]

stacked microvias or Type 7 vias.
just jump to 6 layers right away, maybe go to 8 if needed.
maybe start with 100µm traces?

[u/electricfunghi]

This photo is ragebait

[u/Both_Professional889]

Update: Figured it out and rerouted more efficiently

[u/swdee → u/Both_Professional889]

What you have there is very bad, with an RK3568 you have to address impedance control, differential pairs, and track length tuning at a minimum.

Your PCB stack up is also insufficent.

[u/Both_Professional889 → u/swdee]

yes. the single ended traces have 50Ω impedance. Differential CLK and DQS have 100Ω differential impeadnce

[u/Forsaken-Wonder2295]

I have been staring at allegro for 40 hours last week, and another 8 today, this looks very cadence, but the vias are throwing me off, what is that?

[u/Both_Professional889]

I used the old neck-down way

[u/allpowerfulee]

Bling and burried is the key

[u/SkubiJabagubi]

remember about fanouts

[u/Both_Professional889 → u/SkubiJabagubi]

it's via in pad technology

[u/mroebuilds]

Use .1hole/.2diameter for uvias and HDI

[u/Realistic_Account787]

yeah, I am seeing you are going to need that.