Shop OBEX P1 Docs P2 Docs Learn Events
HELP - SOIC 28 in a TSSOP outline (found in Propeller Project Board USB) — Parallax Forums

HELP - SOIC 28 in a TSSOP outline (found in Propeller Project Board USB)

Alex.StanfieldAlex.Stanfield Posts: 198
edited 2014-04-04 09:36 in General Discussion
Has anyone successfully used a soic 28 chip on Parallax's Propeller Project Board?

The board has a TSSOP layout for smd chips but the reason I ask is because the chip I'm planning to buy has a soic 28 with lead spacing of 1,27mm while the board has 0,65mm spacing. They are not multiples so rather than guessing how hard it is to match them I thought asking around if it's possible based from experience.

Thanks in advance.

Alex

Comments

  • Hal AlbachHal Albach Posts: 747
    edited 2014-04-03 14:08
    SOIC leads land on every other pad on my Prop Project Board - USB. However, your SOIC-28 may be too wide so only one side of the chip will make contact. On my board the width from pin 1 to the opposite pin is about 8.9 mm. I have some SOIC-28 that are 10.55 mm wide and will not fit.
  • Alex.StanfieldAlex.Stanfield Posts: 198
    edited 2014-04-03 15:09
    Hal Albach wrote: »
    SOIC leads land on every other pad on my Prop Project Board - USB. However, your SOIC-28 may be too wide so only one side of the chip will make contact. On my board the width from pin 1 to the opposite pin is about 8.9 mm. I have some SOIC-28 that are 10.55 mm wide and will not fit.

    Your right Hal, I was only looking at pin spacing on the larger dimension :tongue:

    The board's spec says it has 8.7mm width max and that will leave virtually no space to solder the 9.5mm separated pins.

    Thanks for the warning!! Will have to take the DIP version...

    Alex
  • LawsonLawson Posts: 870
    edited 2014-04-03 19:40
    Alex.Stanfield wrote: »
    Your right Hal, I was only looking at pin spacing on the larger dimension :tongue:

    The board's spec says it has 8.7mm width max and that will leave virtually no space to solder the 9.5mm separated pins.

    Thanks for the warning!! Will have to take the DIP version...

    Alex

    If the chip is too wide, you can fold the pins under the package and solder it down. The pins are soft enough to bend that far once, and this will make the chip 3-4mm narrower.

    Marty
  • PropGuy2PropGuy2 Posts: 360
    edited 2014-04-03 20:08
    Already tried the folded under pin thing, big mistake. You can not get enough heat to solder the pin without lifting the PCB trace - and/or get a nice solder bridge in the process.
  • LawsonLawson Posts: 870
    edited 2014-04-04 09:36
    PropGuy2 wrote: »
    Already tried the folded under pin thing, big mistake. You can not get enough heat to solder the pin without lifting the PCB trace - and/or get a nice solder bridge in the process.

    Solder bridges are really easy to fix with solder-wick and flux. The joints actually look better after the fix. (so a good strategy with small joints is to glob on the solder and wick up the extra) A temperature controlled Iron helps with lifting PCB traces. I've had the pleasure of using one of Metcal's fancy irons, haven't lifted a PCB trace in years due to that iron.

    Marty
Sign In or Register to comment.