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From: Robert Baer on 8 Jun 2010 03:05
Bill Sloman wrote:
> On Jun 7, 5:17 pm, Javad Benhangi <benhan...(a)gmail.com> wrote:
>> Thank you everybody.
>> I have a question on PCB manufacturing. I have designed an eight layer
>> board (Top Signal | Power Plane | Gnd | Mid1 Signal | Gnd | Mid 2
>> signal | Gnd | Bottom Signal).
>> I have some problems with the PCB board. There are five BGA chips on
>> it that according to their montage profile the temperature should
>> reach up to 260 degrees centigrade but the board color and its shape
>> changes as the temperature reaches 220. When I send the problem to the
>> PCB manufacture they said that ere made as regular FR4 material and
>> tin-lead finish and it shouldn�t use in using RoHS temperature
>> profile. I think they should let me know about possible board montage
>> problem and ask me about this option before start manufacturing it
>> because I said them that this is the first experience of mine.
>> Anyway, I�m going to reorder the board but I really don�t know what
>> possible options for the board manufacturing are. What I know is just
>> that A) the board should stand temperature over 260. B) The board
>> should stand multiple montages and de-montage process As the frequency
>> if high, what kind of FR4 board is the best? What is the PCB board
>> electrical test report like? They said to me that they have
>> electrically tested the board but the board had some manufacturing
>> fault?
>
> FR4 is a specification for epoxy-bonded glass-fibre board materials.
> If you want a board that can survive higher temperatures, polyimide
> bonded glass fibre can do better.
>
> You need to search on printed circuit baord materials. The Wikipedia
> entry isn't all that helpful
>
> http://en.wikipedia.org/wiki/Printed_circuit_board
>
> and the manufactureres web sites aren't always all that intelligible
>
> http://www2.dupont.com/Packaging_and_Circuits/en_US/products_services/pcb/index.html#laminate
>
> http://www.viasystems.com/technology/pcb-materials.html
>
> --
> Bill Sloman, Nijmegen

Err..polyimide sops up moisture.
Better yet, use Megtron 6; R-5775K and R-5670K, from Matrix USA.
I use that material for units that i GUARANTEE reliable operation to
200C.
From: Bill Sloman on 8 Jun 2010 07:57
On Jun 8, 12:52 am, "k...(a)att.bizzzzzzzzzzzz"
<k...(a)att.bizzzzzzzzzzzz> wrote:
> On Mon, 7 Jun 2010 08:17:43 -0700 (PDT), Javad Benhangi <benhan...(a)gmail.com>
> wrote:
>
> >Thank you everybody.
> >I have a question on PCB manufacturing. I have designed an eight layer
> >board (Top Signal | Power Plane | Gnd | Mid1 Signal | Gnd | Mid 2
> >signal | Gnd | Bottom Signal).
>
> Why so many grounds?  You're wasting money.

Or avoiding cross-talk and reflections. With fast signals you really
do need buried ground planes between buried signal layers.

--
Bill Sloman, Nijmegen
From: Nial Stewart on 8 Jun 2010 09:08
> I have a question on PCB manufacturing. I have designed an eight layer
> board (Top Signal | Power Plane | Gnd | Mid1 Signal | Gnd | Mid 2
> signal | Gnd | Bottom Signal).


Is it really a 9 layer board?

I'd talk with your assembly house to see what temperatures the boards are
really seeing, then talk to your board house and specify a material that
can handle that temperature (and re-work)?

And FR4 != FR4, there are all sorts of variants with different thermal
properties (improved for lead free assembly).


Nial.





From: krw on 8 Jun 2010 18:21
On Tue, 8 Jun 2010 04:57:22 -0700 (PDT), Bill Sloman <bill.sloman(a)ieee.org>
wrote:

>On Jun 8, 12:52�am, "k...(a)att.bizzzzzzzzzzzz"
><k...(a)att.bizzzzzzzzzzzz> wrote:
>> On Mon, 7 Jun 2010 08:17:43 -0700 (PDT), Javad Benhangi <benhan...(a)gmail.com>
>> wrote:
>>
>> >Thank you everybody.
>> >I have a question on PCB manufacturing. I have designed an eight layer
>> >board (Top Signal | Power Plane | Gnd | Mid1 Signal | Gnd | Mid 2
>> >signal | Gnd | Bottom Signal).
>>
>> Why so many grounds? �You're wasting money.
>
>Or avoiding cross-talk and reflections. With fast signals you really
>do need buried ground planes between buried signal layers.

Idiot.
From: Bill Sloman on 8 Jun 2010 18:58
On Jun 9, 12:21 am, "k...(a)att.bizzzzzzzzzzzz"
<k...(a)att.bizzzzzzzzzzzz> wrote:
> On Tue, 8 Jun 2010 04:57:22 -0700 (PDT),Bill Sloman<bill.slo...(a)ieee.org>
> wrote:
>
> >On Jun 8, 12:52 am, "k...(a)att.bizzzzzzzzzzzz"
> ><k...(a)att.bizzzzzzzzzzzz> wrote:
> >> On Mon, 7 Jun 2010 08:17:43 -0700 (PDT), Javad Benhangi <benhan...(a)gmail.com>
> >> wrote:
>
> >> >Thank you everybody.
> >> >I have a question on PCB manufacturing. I have designed an eight layer
> >> >board (Top Signal | Power Plane | Gnd | Mid1 Signal | Gnd | Mid 2
> >> >signal | Gnd | Bottom Signal).
>
> >> Why so many grounds? You're wasting money.
>
> >Or avoiding cross-talk and reflections. With fast signals you really
> >do need buried ground planes between buried signal layers.
>
> Idiot.

Really? So what's your alternative approach? The stuff you post
doesn't suggest that you've ever actually worked with signals fast
enough to rub your nose in transmission line problems, and you are
obviously too stupid to realise signals with rise times around a
nanosecond or faster need this kind of attention.

You do claim to work with current programmable logic devices, and some
of today's parts are quite fast enough to make signal integrity
problems tolerably salient - obviously not the ones that you are
trusted to work with.

--
Bill Sloman, Nijmegen
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