[SI-LIST] Re: why use oblong pad?

There is not much difference between the two - feel free to use a
rectangle if you want, or are perhaps restricted by your CAD tool.

However, an oblong pad reduces the board area necessary for the pad,
and can help on very dense layouts when you have lots of signals
routed on the component side(s). It also helps minimise the chance
of less-than-90 degree corners (between track and pad) if you route
out of the pad at an angle, which is a good thing for manufacturing.

What probably makes the most difference, is an oblong shaped 'eye'
in the solder paste stencil (even if the copper pad is rectangular!).
Why? Well, solder paste is made of fine balls of metal alloy (which
later melt, but at application have a finite size) in a flux base.
And sharp corners offer convenient niches for paste to be 'caught'
in, which in turn:

a) makes stencil cleaning harder, increasing the chance that old paste
   will be re-applied at a later batch, or simply reduce the opening,
   by hardening in the stencil, which reduces the amount of paste
   applied in a later batch;

b) can also, with small components (and therefore small stencil
   openings), make a clean application more difficult - applied
   paste is more likely to be lifted back off the board when the
   solder stencil is removed.

The importance of this point depends upon the specific layout and
other factors, eg. quantity of boards, quality/thickness of stencil,
quality/type of paste, size of pads, etc. If you are restricted by
CAD to rectangular, don't worry - IF it really proves to be a problem,
the solder paste stencil manufacturer can substitute oblongs for
rectangles by editing your Gerber files.

Hope this helps.
____________________________________
Sol Tatlow, M.Eng. (Oxon)
ProDesign Electronic & CAD Layout GmbH
Product Developer
Albert-Mayer-Str. 16
D-83052 Bruckmuehl
Phone: +49 (0) 8062-808-302
Fax:   +49 (0) 8062-808-333
Mailto:sol.tatlow@xxxxxxxxxxxxxxxxxxxx
www.prodesign-europe.com
____________________________________=20

-----Urspr=FCngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
Im Auftrag von jagaveer25
Gesendet: Donnerstag, 28. April 2005 11:58
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] why use oblong pad?

hi=20

i am learning pcb design
usually oblong pad is used in design, i would like to know why=20
rectangle pad is not used?
or

Difference between oblong pad and Rectangle Pad?

any one tell me plz.........


V.jagaveer

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