FreeLists / si-list / [SI-LIST] Re: 4 Ghz PCB

["Shawn Arnold" <shawn@xxxxxxxxxxxxxxxxxxxxxxxx>]

Hi Dan,

I am currently working on a similar problem and can offer a couple of
insights and request additional advice from those on the list.

The PCB we are doing is also 4Ghz, the 100 ohm diff pair is 2" long,
micro strip construction, high temp FR-4, 4 layer, soldermask over the
traces, .031 thick, one via per line.

Using standard construction, HASL finish and leaded assembly, the PCB
performed flawlessly, beautiful eye diagram. As soon as we went
lead-free, the wheels fell off. 

Using an immersion Silver finish and no-clean assembly, the assembly
residue on the traces caused significant scatter and the eye started to
separate. We ran the same assemblies with a lead-free clean process and
the scatter disappeared leaving the eye separation.

Upon further inspection, we noticed that the first successful PCBs had
soldermask plugged vias and the second PCBs had them open. Additionally,
the fabrication stack-up was slightly different in that the first PCB
used two pieces of pre-preg and the second PCB used a single ply for the
layer 1 to 2, spacing.

Hope this helps identify potential problems for you and provides enough
information for some feedback and direction from others on this list.

Regards,
Shawn

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of david stern
Sent: Thursday, July 14, 2005 7:34 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] 4 Ghz PCB


hi
 
I have to design pcb with 50 Ohm differential pairs working at 4 Ghz.
 
How to desin and simulate the differential pairs at 4 Ghz?
 
where can I find usefull links about it ?(there are a lot links and i
don't have time to 
 
look aat every one)
 
THANKS
 
David s
 
 
__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com 

------------------------------------------------------------------
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:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://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:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://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