SMT Land Pattern Variations

Discussion in 'General Electronics Chat' started by tracecom, Mar 29, 2015.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
    Although I have laid out some PCBs with a few SMT components, I am only now designing one that includes more SMT than through hole components. Because I will have to hand solder the first few, I am using no components smaller than 0805.

    At first, I thought that all 0805 components used the same land patterns, but in looking at the datasheets, it seems that LEDs, resistors, ceramic capacitors, and ferrite beads all use slightly different patterns even though they are all 0805. Does it matter, or is there a "common" pattern that will work for all SMT components of the same size?

  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Just slight variations between manufacturers.. (opinions even in what should be/is standardized)
    In general they should all work just fine though..
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    Welcome to the club.

    I discovered that SOIC-8 SMD's were not all the same a few years ago. Fortunately, the differences didn't ruin that project, but I learned. I always check today to be sure the recommended pad layout for the device I am using is compatible with what I used from the CAD software. My design library (Eagle) has grown quite a bit since that realization. I have not had a problem with two-lead devices, so long as I pay attention to re-flow versions vs. other versions of the devices.

  4. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
    Thanks for the input.

    Here is a table that shows the variety of patterns I will be using for 0805 components, if I go by the manufacturers' recommendations. Dimensions are in millimeters.

    0805 SMT Pattern Variations.PNG
  5. RichardO

    Well-Known Member

    May 4, 2013
    I have mentioned this on other threads but I will repeat it here. Do not make the pads larger than the recommended sizes. If you do, the parts will tombstone (stand on one end) when reflow soldered. This is apparently caused by the extra surface tension from excess solder on the pad.
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    A tombstone part is caused not by pad size but a difference in pad sizes, or rather the difference in solder on the pads. The pad with more solder exerts a greater surface tension pull. It's similar to playing with water drops only here you have (literally!) molten metal.

    Back before surface mount was much used we built parts with hand dispensed solder and reflowed on a heat column under a microscope. A probe tip was kept handy to both move solder around and to push down the occasional tombstoned part.