BGA soldering and ground plane

I have designed a 6 layer board using a 256 ball Atmel BGA chip
(AT91RM9200). It consists of two internal power layers, 2 internal
signal layers and two heavily copper filled outer layers with
virtually no tracks. The stackup has the Toplayer, Signal layer then
Power layers very close together with a 1mm core. I  am seeing a high
level of failures due to the BGA chip solder balls not melting (Lead
free manufacture). My manufacturer tells me that this is because I
have a solid ground plane on the two outer layers of the PCB,  though
not underneath the solder balls on the top outer layer. They state
this is a large thermal mass and stopping the bga heating properly.
The copper planes are there for good EMC practice so I am loath to
remove them, however if this really is the cause of the problem I will
have to. Has anybody else come across this problem or can offer any
solutions, thanks?

"sjones@scannex.co.uk" wrote:
> 
> I have designed a 6 layer board using a 256 ball Atmel BGA chip
> (AT91RM9200). It consists of two internal power layers, 2 internal
> signal layers and two heavily copper filled outer layers with
> virtually no tracks. The stackup has the Toplayer, Signal layer then
> Power layers very close together with a 1mm core. I  am seeing a high
> level of failures due to the BGA chip solder balls not melting (Lead
> free manufacture). My manufacturer tells me that this is because I
> have a solid ground plane on the two outer layers of the PCB,  though
> not underneath the solder balls on the top outer layer. They state
> this is a large thermal mass and stopping the bga heating properly.
> The copper planes are there for good EMC practice so I am loath to
> remove them, however if this really is the cause of the problem I will
> have to. Has anybody else come across this problem or can offer any
> solutions, thanks?

Try etching away most of the outer layers, making them effectively
a grid of pinholes (to the frequencies of interest).  I suspect you
should be easily able to remove 50% of the heat absorbing problem,
without altering the shielding effects.

-- 
 [mail]: Chuck F (cbfalconer at maineline dot net) 
 [page]: <http://cbfalconer.home.att.net>
            Try the download section.

On 5 Nov, 15:23, "sjo...@scannex.co.uk" <sjo...@scannex.co.uk> wrote:
> I have designed a 6 layer board using a 256 ball Atmel BGA chip
> (AT91RM9200). It consists of two internal power layers, 2 internal
> signal layers and two heavily copper filled outer layers with
> virtually no tracks. The stackup has the Toplayer, Signal layer then
> Power layers very close together with a 1mm core. I  am seeing a high
> level of failures due to the BGA chip solder balls not melting (Lead
> free manufacture). My manufacturer tells me that this is because I
> have a solid ground plane on the two outer layers of the PCB,  though
> not underneath the solder balls on the top outer layer. They state
> this is a large thermal mass and stopping the bga heating properly.
> The copper planes are there for good EMC practice so I am loath to
> remove them, however if this really is the cause of the problem I will
> have to. Has anybody else come across this problem or can offer any
> solutions, thanks?

Are they leaving enough time for the heat to propagate through the
"thermal mass" to the component side? Is there a problem in letting
the components cook for a bit longer?

--
James

On Wed, 5 Nov 2008 15:09:23 -0800, CBFalconer wrote
(in article <491227A3.AFFA133F@yahoo.com>):

> "sjones@scannex.co.uk" wrote:
>> 
>> I have designed a 6 layer board using a 256 ball Atmel BGA chip
>> (AT91RM9200). It consists of two internal power layers, 2 internal
>> signal layers and two heavily copper filled outer layers with
>> virtually no tracks. The stackup has the Toplayer, Signal layer then
>> Power layers very close together with a 1mm core. I  am seeing a high
>> level of failures due to the BGA chip solder balls not melting (Lead
>> free manufacture). My manufacturer tells me that this is because I
>> have a solid ground plane on the two outer layers of the PCB,  though
>> not underneath the solder balls on the top outer layer. They state
>> this is a large thermal mass and stopping the bga heating properly.
>> The copper planes are there for good EMC practice so I am loath to
>> remove them, however if this really is the cause of the problem I will
>> have to. Has anybody else come across this problem or can offer any
>> solutions, thanks?
> 
> Try etching away most of the outer layers, making them effectively
> a grid of pinholes (to the frequencies of interest).  I suspect you
> should be easily able to remove 50% of the heat absorbing problem,
> without altering the shielding effects.
> 
> 

Are you forced to use ROHS? It stinks. Safety critical and aerospace systems 
are exempt -- tin whiskers and all that.

(Does elemental lead actually hurt anyone?)

-- Charlie Springer

Hi,

> free manufacture). My manufacturer tells me that this is because I
> have a solid ground plane on the two outer layers of the PCB,  though
> not underneath the solder balls on the top outer layer. They state
> this is a large thermal mass and stopping the bga heating properly.

Use another manufacturer. I suppose he uses an old infrared reflow oven. 
For this setup, you get best results with vapor phase soldering. We 
often have such setups, and it is no problem.

best regards
Thorsten Trenz

--
www.trenz-electronic.de

Charlie Springer wrote:
> On Wed, 5 Nov 2008 15:09:23 -0800, CBFalconer wrote
> (in article <491227A3.AFFA133F@yahoo.com>):
> 
>> "sjones@scannex.co.uk" wrote:
>>> I have designed a 6 layer board using a 256 ball Atmel BGA chip
>>> (AT91RM9200). It consists of two internal power layers, 2 internal
>>> signal layers and two heavily copper filled outer layers with
>>> virtually no tracks. The stackup has the Toplayer, Signal layer then
>>> Power layers very close together with a 1mm core. I  am seeing a high
>>> level of failures due to the BGA chip solder balls not melting (Lead
>>> free manufacture). My manufacturer tells me that this is because I
>>> have a solid ground plane on the two outer layers of the PCB,  though
>>> not underneath the solder balls on the top outer layer. They state
>>> this is a large thermal mass and stopping the bga heating properly.
>>> The copper planes are there for good EMC practice so I am loath to
>>> remove them, however if this really is the cause of the problem I will
>>> have to. Has anybody else come across this problem or can offer any
>>> solutions, thanks?
>> Try etching away most of the outer layers, making them effectively
>> a grid of pinholes (to the frequencies of interest).  I suspect you
>> should be easily able to remove 50% of the heat absorbing problem,
>> without altering the shielding effects.
>>
>>
> 
> Are you forced to use ROHS? It stinks. Safety critical and aerospace systems 
> are exempt -- tin whiskers and all that.
> 
> (Does elemental lead actually hurt anyone?)
> 

Much of ROHS is disproportionally strict, and it's implementation and 
integration has caused endless problems.  But many of the restrictions 
are for good reasons (environmental protection, and human safety) - 
"lead-free" is only one aspect.  It's the part that causes most trouble 
for manufacturers, but it is other ROHS-banned substances that are more 
poisonous.  Also note that although elemental lead is not a danger 
(unless you *eat* old pcbs), it reacts with all sorts of other gunk in 
landfills, and seeps into the water table as compounds which *are* 
poisonous.

The real problem with ROHS (and similar initiatives in the far east and 
parts of the USA) was the implementation - the powers behind them had a 
naive and childish belief in the power of capitalism and "the market" to 
solve any problem given enough advance warning.  If they'd done the 
research first, *then* made the rules, we'd have had a far more reliable 
and economic solution.

"Charlie Springer" <RAM@regnirps.com> wrote in message 
news:0001HW.C53D224300B2D5E0F02845B0@news.nw.centurytel.net...
> On Wed, 5 Nov 2008 15:09:23 -0800, CBFalconer wrote
> (in article <491227A3.AFFA133F@yahoo.com>):
>
>> "sjones@scannex.co.uk" wrote:
>>>
>>> I have designed a 6 layer board using a 256 ball Atmel BGA chip
>>> (AT91RM9200). It consists of two internal power layers, 2 internal
>>> signal layers and two heavily copper filled outer layers with
>>> virtually no tracks. The stackup has the Toplayer, Signal layer then
>>> Power layers very close together with a 1mm core. I  am seeing a high
>>> level of failures due to the BGA chip solder balls not melting (Lead
>>> free manufacture). My manufacturer tells me that this is because I
>>> have a solid ground plane on the two outer layers of the PCB,  though
>>> not underneath the solder balls on the top outer layer. They state
>>> this is a large thermal mass and stopping the bga heating properly.
>>> The copper planes are there for good EMC practice so I am loath to
>>> remove them, however if this really is the cause of the problem I will
>>> have to. Has anybody else come across this problem or can offer any
>>> solutions, thanks?
>>
>> Try etching away most of the outer layers, making them effectively
>> a grid of pinholes (to the frequencies of interest).  I suspect you
>> should be easily able to remove 50% of the heat absorbing problem,
>> without altering the shielding effects.
>>
>>
>
> Are you forced to use ROHS? It stinks. Safety critical and aerospace 
> systems
> are exempt -- tin whiskers and all that.
>
> (Does elemental lead actually hurt anyone?)

Yes. It affects mental development in children. Same reason it was removed 
from fuel and paint.

Peter 

On Mon, 10 Nov 2008 08:31:05 -0000, "Peter Dickerson"
<first.last@REMOVEtiscali.co.uk> wrote:

<snip>
>>
>> (Does elemental lead actually hurt anyone?)
>
>Yes. It affects mental development in children. Same reason it was removed 
>from fuel and paint.

uhhh, those both had lead compounds -  not elemental lead
-- 
ArarghMail811 at [drop the 'http://www.' from ->] http://www.arargh.com
BCET Basic Compiler Page: http://www.arargh.com/basic/index.html

To reply by email, remove the extra stuff from the reply address.

<ArarghMail811NOSPAM@NOT.AT.Arargh.com> wrote in message 
news:s5ufh4dg0nqk0d9jhvurt3v1o8l06n7d4g@4ax.com...
> On Mon, 10 Nov 2008 08:31:05 -0000, "Peter Dickerson"
> <first.last@REMOVEtiscali.co.uk> wrote:
>
> <snip>
>>>
>>> (Does elemental lead actually hurt anyone?)
>>
>>Yes. It affects mental development in children. Same reason it was removed
>>from fuel and paint.
>
> uhhh, those both had lead compounds -  not elemental lead

Do you think elemental lead stays that way indefinitely?

Peter 

"Peter Dickerson" <first.last@REMOVEtiscali.co.uk> wrote:

>> Are you forced to use ROHS? It stinks. Safety critical and aerospace 
>> systems
>> are exempt -- tin whiskers and all that.
>>
>> (Does elemental lead actually hurt anyone?)
>
>Yes. It affects mental development in children. Same reason it was removed 
>from fuel and paint.

And how does one measure mental development of children with any accuracy? 

Even when you do find correlation between lead content of children and lack
of mental development (which some but not all studies have found) how do
you determine that the lead was causal and not that lack of mental
development or more likely other factors which led to mis-measurement of
mental development causes an increase in lead content of children? 


--