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From: Javad Benhangi on 7 Jun 2010 11:17
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?
Many thanks
From: Bill Sloman on 7 Jun 2010 11:51
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
From: Tony on 7 Jun 2010 12:25
Javad Benhangi 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?
> Many thanks

As you say it is your first time, but the professional world does not
care about that. You have made some critical errors which are well
known areas to avoid to those with experience. You can get some
responses on here, but it sounds like you either need a consultant or do
alot more research on assembly technology.

I agree you cannot strictly use HASL with lead free BGAs. HASL has
pretty much died out for Rohs applications and you should not mix it
with lead free stuff, if you want HASL for some critical Rohs exempt
application then you need tin/lead based BGAs aswell as they use solder
balls, other items with lead free finished terminals can be mixed easily
enough.

I use normal FR4 (Tg135 grade material) for my 4 layer lead free boards
with 2 lead free BGAs without any problems, but BGA replacement more
than once would be a challenge (higher Tg needed for that). I do
specify a Hi temperature OSP coating on copper as the normal OSP does
not have much of a lifetime after 1st reflow and there is another solder
process further down the line. OSP is also nice flat for the assembly.
I am a production Engineer not a design Engineer, the designers do not
know this stuff (usually), they have other priorities. I would also not
take the 260C soldering requirement to literally unless your application
is really critical, are you sure its not just a peak temp. My boards
don't go over 250C typically (Tier 1 CEM).

Warping under reflow is normally more due to uneven heating or
unbalanced copper across the layers or across the PCB area. You could
consider using crosshatch for ground plane and filling in any empty
spaces with crosshatch plane or unconnected crosshatch.

--
Tony
From: oparr on 7 Jun 2010 14:12
>but the board color and its shape
>changes as the temperature reaches 220.

A typical tin-lead solder paste may have a suggested peak temperature
of 210-225 in its reflow profile. So what you are seeing should not
happen with any board IMO. Are you certain about your temperature
measurement accuracy?


On Jun 7, 11:17 am, Javad Benhangi <benhan...(a)gmail.com> wrote:
>
From: krw on 7 Jun 2010 18:52
On Mon, 7 Jun 2010 08:17:43 -0700 (PDT), Javad Benhangi <benhangi0(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.

>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.

You *must* be going above 220, more like 260 or greater.

>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.

We use, I think, standard board stock on a RoHS process without problems. It
took some time to learn and we did have some component problems but everything
is smooth now. Our temperature profile hits 250C for something like ten
seconds. We're looking into a better oven to control this tighter.

Before we got the process tuned we had some board discoloration, mainly a
board with a white solder mask came out sorta pink. Still worked, though.

>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?

They tested the board and sent you bad ones? Sounds like you need a new board
house. Some are pretty bad.
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