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Can I solder a QFN-44pin propeller using solder paste? — Parallax Forums

Can I solder a QFN-44pin propeller using solder paste?

Tony_tsiTony_tsi Posts: 98
edited 2011-12-10 03:33 in Propeller 1
I am trying to finish my UV exposure unit this week (more info here http://www.tonytronix.com/myprojects/uvexposure.html) I have some experience with soldering QFP chips with paste but have never tried a QFN. Parallax is out of 44 pin QFP chips. So my options are as follows:
  1. use a QFN and solder paste (reflow oven)
  2. use a QFN and socket (I don't know a good place to get a socket without having to pay $6.00 shipping for a $1.00 part)
  3. wait for the QFP to be in stock.
I am fairly new to smd. thanks for any suggestions or help.

Comments

  • LeonLeon Posts: 7,620
    edited 2011-12-09 15:44
    I've soldered QFN chips with a soldering iron, I put a large via in the central pad and feed solder into it with the iron tip. Metcal equipment makes it easier.
  • kwinnkwinn Posts: 8,697
    edited 2011-12-09 15:50
    Your best bet would be # 1 if your board lay out is for a QFN. If you already have a board laid out for a QFP the pads will not line up with a QFN (0.65 vs 0.8mm spacing). The $7.00 for a socket may not be such a bad deal. Maybe buy more than one.
  • Cluso99Cluso99 Posts: 18,069
    edited 2011-12-09 15:50
    Check with Parallax - most likely stock has just not been added in. This seems to happen occasionally. Digikey also stock them (not checked today).

    Solder paste is normal for all parts. So I presume you mean using a soldering iron. I have not tried QFNs yet but others have successfuly done this. You do need to be more careful with the amount of paste applied.
  • Tony_tsiTony_tsi Posts: 98
    edited 2011-12-09 15:54
    I did not know they had a metal pad in the center. I have traces running under the chip and I don't have a solder mask on my pcb. This could be a problem.
  • Tony_tsiTony_tsi Posts: 98
    edited 2011-12-09 15:56
    kwinn wrote: »
    Your best bet would be # 1 if your board lay out is for a QFN. If you already have a board laid out for a QFP the pads will not line up with a QFN (0.65 vs 0.8mm spacing). The $7.00 for a socket may not be such a bad deal. Maybe buy more than one.
    The board was laid out with ultiboard and I have not etched it yet if need be i can change the foot print.
  • Tony_tsiTony_tsi Posts: 98
    edited 2011-12-09 16:05
    I found one at digikey.
  • Tony_tsiTony_tsi Posts: 98
    edited 2011-12-09 16:08
    Does any one know if there is a metal plate in the center of the QFP. If so I will forced to use a socket with a QFN because I have traces running under the micro controller and I do not have a solder mask on the board.
  • LeonLeon Posts: 7,620
    edited 2011-12-09 16:12
    The data sheet has all the information you need for PCB design.
  • MacTuxLinMacTuxLin Posts: 821
    edited 2011-12-09 23:07
    As Leon mentioned, the Prop1 datasheet has all the information you need. I have a 2 boards designed for QFN. If you're using reflow, make sure you bake it before hand.
  • WBA ConsultingWBA Consulting Posts: 2,935
    edited 2011-12-09 23:58
    There is a metal pad on the bottom of the QFN. The best way to solder the pad is with a windowed stencil to apply four squares of paste on the pad that would be on the PCB. Using pads for the leads that extend past the perimeter of the QFN will aid in any necessary rework because the edges of the QFN are not actual solder terminals. They are just the raw edges from the carrier used to manufacture the QFN package. You can see an example pad layout on my M44D40+ PCB. I use a 5 mil thick stainless steel stencil to apply no-clean solderpaste for reflow soldering.
  • TubularTubular Posts: 4,708
    edited 2011-12-10 03:33
    Tony_tsi wrote: »
    Does any one know if there is a metal plate in the center of the QFP. If so I will forced to use a socket with a QFN because I have traces running under the micro controller and I do not have a solder mask on the board.

    No, there is no metal plate under the QFP. You can put traces and vias under there.

    Sometimes this makes the design more compact than a QFN based design (where you can't put anything under except a ground pad).
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