[PCB_FORUM] Re: micro vias or thin traces
- From: "Mitch S. Morey" <cadpro2k@xxxxxxxxxx>
- To: icu-pcb-forum@xxxxxxxxxxxxx
- Date: Tue, 4 Apr 2006 09:57:20 -0700 (PDT)
Hi Sam,
Couple things. I've been doing these .5mm BGAs almost exclusively now.
1) You should be able to 'skinny' up the BGA pads to go with 3mil traces.
That's where I am. Also, going with 3mil traces your fab shop will want to
use either 3/8oz CU or 1/4oz CU on the outer layers (or whatever layer you
go to 3mils on). Ask them. Mine wants to use 1/4oz, but I want 3/8oz. They
can do 3/8oz.
2) uVia (microvia) tchnology is VERY common for these minimum pitch BGAs.
I'm using 5mil lazer/10mil pads to breakout the pads.
3) If you do happen to go Via-in-Pad on the boards (and I have, at .4mm
pitch), make sure you mark the area on your fab drawing, and state
something like "In area detailed (the BGA pad area), plate pad surfaces
flat." This will leave a VERY flat mounting surface for the BGA.
4) For assembly, make sure you've accounted for ANYTHING that can "Stress"
the BGA once assembled. I have panels that utilized V-scoring to separate
the individual boards. After the parts are assembled, the assembly shop
has a 'holding/breaking' apparatus to separate the boards. This holds the
boards firm while they're being broken apart. We had major reworking going
on until we found out people were short cutting the process, and breaking
them without the fixture. BAD! Very BAD! These boards do not take well to
ANY stress induced on the boards.
5) Also! Be careful of what's Lead-Free and what's not. Are the .5mm BGAs
you're using Lead-Free? Find out. Lots can go wrong.
Good day.
Mitch
> Thanks for the response from everyone. We found a board house who will
> drill 12 mil pads with 8 mil drill and it will be via in pad technology.
> Sam
>
> -----Original Message-----
> From: westfeldt <westfeldt_nbcd@xxxxxxxxx
> Subject: [PCB_FORUM] Re: micro vias or thin traces
>
>
> I have done a few of these, but never without microvias. 5 mil laser
> drills. pads anywhere from 10 to 13 mils.
>
> Patrick Westfeldt, Jr.
> 720-406-0887
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