Subject: | |
From: | |
Reply To: | |
Date: | Wed, 15 Dec 2004 11:26:41 +1100 |
Content-Type: | text/plain |
Parts/Attachments: |
|
|
Just some further findings on this particular problem;
There are four through hole connector pads (A,B,C,D) in a row, each pad
0.8 inches from the next pad.
There is a 6 thou, half ounce track (same internal layer) running in
parallel with the four pins, about 100 thou from the pads.
The four pins are connected to the pads with stubs. IE: the traces do
not go through the pads
The resistance measurements are as follows:
A to B = 1.2 ohms
B to C = 1.2 ohms
C to D = 1.2 ohms
A to C = 2.5 ohms
B to D = 2.5 ohms
A to D = 3.7 ohms
Which makes the trace stub and pad/via resistance approx 0.05 ohms
And the parallel trace resistance between any two adjacent pins approx
1.2 ohms
The other internal layer is the same, but the A to D resistance is 2.4
ohms
Some other PCBs show approx identical resistances
While others have different resistance but the same ratios
Some are OK
None of the external traces show this effect. Even those going through
vias from the top to the bottom of the PCB.
regards,
Phil.
-----Original Message-----
From: TechNet Behalf Of Valerie St.Cyr
Sent: Tuesday, 14 December 2004 1:30 AM
To: [log in to unmask]
Subject: Re: [TN] Resistive internal layers
Here's a thought: if all the tracks on a particular layer exhibit high
resistance then likely that layer was either reworked or may have
excessive oxide treatment. If, however, it is only the one track, then
the
problem is with the track itself. In the past we have found that a
"dishdown" or nick or "mousebite", anything that reduces the volume of
copper in a spot on the track is now a "bottleneck" that increases the
line resistance. The other possibility is that a via in that net has low
copper or copper voiding, which would also show up as high resistance on
the net.
To really root cause the problem would require doing some cross-sections
...
Good luck and let us know what you find.
Regards, Valerie
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
|
|