[SI-LIST] Re: Heat issue in PCB's
- From: "Barnes, Heidi" <heidi.barnes@xxxxxxxxxx>
- To: "sunil bharadwaz" <sunil_bharadwaz@xxxxxxxxx>, "SI LIST" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 10 Oct 2008 09:17:19 -0500
Hi Sunil,
Going to 2oz copper helps thermally, but fabrication and etching tolerances can
get more difficult. The PCB industry is quite comfortable with 1oz and this is
usually what is selected to help with heat dissipation.
The difference that you are seeing between fab vendors is probably in the vias.
Via plating can have a significant effect on getting the heat to these large
copper ground planes. The trick with vias and one that is often overlooked is
that the minimum 0.7mils of plating in a via is not the best for thermal and
one should talk with the fabricator to see if this can be increased (~1mil is
not too unreasonable) or like Tim mentioned you need to add more stitching vias
to reduce the sensitivity to via plating thickness.
You could also look at adding Ground fill to the top and bottom signal layers
if there is any room rather then going to 2oz inner copper.
Best Regards,
Heidi
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Nash, Timothy J
Sent: Friday, October 10, 2008 6:31 AM
To: sunil bharadwaz; SI LIST
Subject: [SI-LIST] Re: Heat issue in PCB's
Sunil,
The proportion of copper to dielectric in a PCB's makeup is definitely a factor
with respect to a PCB's ability to reject heat. You are correct in assuming
that if you increase copper thickness it will help in heat rejection. In
extreme cases, you can also add copper planes in the stackup dedicated to
rejecting heat (thermal planes). However, you need to make sure that you give
the heat a place to go by stitching vias between these planes and also between
the planes and the chassis (i.e. to plating under wedgelocks or plating around
tooling holes). Not only will this help EMI/EMC, but it will also serve as a
thermal rejection path.
One thing to keep in mind - I have seen stackups that had so much copper (with
respect to the dielectric) - that they had trouble reflowing solder - it just
couldn't heat up fast enough.
Hope this helps.
Tim
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of sunil bharadwaz
Sent: Thursday, October 09, 2008 8:15 PM
To: SI LIST
Subject: [SI-LIST] Heat issue in PCB's
Hi ,
I have a four layered PCB ,Sig,Gnd,Pwr & Sig.The gnd & power are 1 Oz copper.
Does the heat dissipation of the PCB's improve , if the thickness of the Power
planes
is increased to 2 oz Cu.Vice versa , does the heat dissipation go bad upon
decreasing
the thickness of the Power planes to 1/2 Oz.
I have two PCB's from two fab houses (Basically same Gerbers).The heat
dissipation from on one of these is bad as the board from the other fab house
seems lot better in this regard.
I'am interested to investigate into this.Pls suggest me the things
to look for here.
Thanks in advance!!
Best regards
Sunil
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
