Are you sure the pad size is due to current capacity and not due power
dissipation of the component. Many components require more area on the
PCB to dissipate the rated power.
----- Original Message -----
From: "Forrester, Michael (H USA)" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, July 20, 2010 5:34 PM
Subject: [TN] SMT PAD Current Capability
I'm a bit confused on how to calculate the current capability of a SMT
pad. We have a 2220 size chip bead that has 8A flowing through it.
Our pad geometry is built per IPC specifications but the manufacturers
datasheet calls out for a PAD twice the width (part max is 10A).
So the question came up, with our current pad geometry (to IPC), what is
the current capability? I understand that it is based on the
cross sectional area of the copper. The current density of copper is
4.02 A/sq-mm. For a 1 oz copper trace the area is
1.4 mils x trace width. But what do I use for a PAD? I have an width,
length, and thickness. For instance I have a SMT pad that
is 1.5mm X 6mm using 1 oz copper with multiple traces coming off of the
pad. What is the current carring capability of that pad?
Or am I thinking about this wrong? Thank you.
Best Regards,
Michael Forrester
Sr. Product Engineer
Siemens Healthcare Diagnostics
101 Silvermine Rd.
Brookfield, CT 06804
PH: (203) 740-6452
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