[gta02-core] Board parameters update

[Álvaro Lopes]

Rene Harder wrote:
> So here are a few comments where i think we can cut costs.

> Is 4 mil really necessary? Most fabs go down to 5-6mil as min.
> Trace/Space width. I believe we can find a fab who can make boards with
> 4mil but that require a more precision fabrication process as well makes
> it electrical and optical test absolutely necessary. Although most fabs
> will require an electrical test for board with equal or more than 6 layers.

No, we can live with 5mil. Unless the RF traces require smaller tracks, but we can overcome that.

> I think for a prototype a regular chemical or HAL tin finish might be
> sufficient or are the any specific reasons why we need ENIG.

> I guess 1080 woven-glass with 65% FR4 epoxy laminate is pretty much
> standard everywhere so shouldn't be too difficult to get. About 1078
> prepreg im not sure, haven't seen it anywhere in the specs so this might
> be only possible within custom specs.

We should get quotes from some manufactures about the prepreg. Actually we need that to properly design RF.

> 140 unique components, that's quite much

I don't think so. There are machines that can handle more than that.

> For solder stop mask and silk screen i think they don't make much of a
> difference in production cost usually you have to pay a small setup fee
> for the whole batch if it's not included.

Define 'small' :)

> A serious problem are blind and buried vias though. They are our killer
> for any standard specs, if I'm not mistaken they require a huge amount
> of extra steps between every lamination process which is impossible to
> do within standard spec. So best would be to stick to PTH vias if that's
> not possible our cost will be probably more than doubled.

PTH vias present other problems too. We can probably like with PTH though, but I'd like at least to have microvias for the FBGA. But all this depends on how we
decide to use the layers.

> Just a an example a board with our size, 6 layer, 6 mil Trace/Space, all
> holes platted through, quantity 15 pcs. is about $80 USD/ per board
> (board outline routing is only rectangle though)


plated through, and filled with insulator or conductor?

> For a board with our current specs 8 layer, ENIG, burried and blind
> vias, we would need to get a custom quote (which usually needs a final
> board layout). But i do think Werner's estimation is not far away from
> the real cost so we would end up around $250-300/per board.
> 
> At the end, i think we should consider that this will be *only* a
> prototype and not a usable phone, so we don't need a lot of gimmicks
> which are not absolutely required.

Yes, but we should get as close as the "final product" as possible.

Álvaro