SMD Footprint Overview

Just found this very useful document:

www.ibselectronics.com/pdf/pa/walsin/smt_notes.pdf

Samuel

Hm.

Read it, can't say that I'm a huge fan. Apart from the fact that it is rather dated (mostly non-RoHS, plus almost nobody does wave soldering any more), they appear to give no rationalization behind the footprints, whereas normally you would adapt footprints with regards to soldering process (manual, normal-density reflow, hi-density reflow).

The footprint collection is a basic starting point, but for more useful detail level I'd suggest looking at the IPC land patterns standardized in IPC-7351. While the standard itself is non-free, several manufacturers have useful excerpts and other documents online (such as this one), and there's even a freeware footprint generator available for download.

JDB.

Philips (NXP) has published a databook "Integrated circuit packages" (document number IC26). It contains dimensions for all IC packages I can imagine. It has also pad dimensions and layouts for both reflow and wave soldering. Plus useful information about thermal design.

Nice pictures and surely informative for SMT newbies.  (I didn't see any pictures of tombstoned parts. )

Most manufacturers provide recommended footprint details in the data sheets, while it is useful to talk with your contract manufacturer too when dealing with oddball parts.

I'm working on a tiny class D chip that has a heatsink on the bottom of the package. That alone is not that unusual (common in BGA), but they call for blind vias and/or vias with tiny drill holes to prevent wicking solder away from the bottom pad. Interesting tradeoff between more vias for heat transfer and less for solder quality...

JR

Lots of chips are moving towards using the bottom pad as a system ground as well since they can bond the grounds directly to it for reduced inductance between ground and the die.  This makes it easier than moving to a larger package and using more pins for ground.

In the future it will probably all be BGA... I am getting too old to prototype this stuff.. It's getting to the point where I have to go straight to a first cut PCB just to check out these parts for suitability. 

I do like how small they are for final production, but first I need a working design, and my old way was to breadboard everything first. 

JR

Nice link Samuel. and in thankful to all of you for the information provided about SMD Footprint.

audiox said:

Philips (NXP) has published a databook "Integrated circuit packages" (document number IC26). It contains dimensions for all IC packages I can imagine. It has also pad dimensions and layouts for both reflow and wave soldering. Plus useful information about thermal design.

Click to expand...

http://www.standardics.nxp.com/packaging/handbook/

I keep seeing the word footprint being used. Now correct me if I'm wrong but isn't this the mark your foot makes say in snow or mud or in freshly laid concrete? How, perish the thought, has it become another hideous 21st century buzz word meaning something that it isn't??

Footprint is commonly used for several things unrelated to human or animal pedal extremities. What it means in the context of "circuit board solder pad layout patterns" seems well understood. Do you have an unambiguous alternative with similar number of syllables or less?

If you want to complain about usage, how do you feel about your carbon footprint?

JR

JohnRoberts said:

Footprint is commonly used for several things unrelated to human or animal pedal extremities. What it means in the context of "circuit board solder pad layout patterns" seems well understood. Do you have an unambiguous alternative with similar number of syllables or less?

If you want to complain about usage, how do you feel about your carbon footprint?

JR

Click to expand...

;D

Well, I flew to Geneva last Saturday, flew back (to England) last night and we fly to Alicante in Spain on Thursday - so much for my carbon footprint!!

However, I do think the English language has gone a little loopy lately!