Fix broken pins on QFP Package

That is how my new HW-0.30-mini Quadcopter Flightcontrol looked prior to the repair:

broken pins

Since a few of the Pads already were delaminated I decided to do a repair instead of soldering in a new CPU. For a repair I would need to get rid of the expoxy mold to directly acces the pins of the leadframe. Initially I was thinking of using a ‘dreml’ tool to remove the exoxy, but watching the Uncaging Microchips talk at 31C3 taught me that using a CO2-Laser will also work.

Those pictures were taken during the laser-removal:

 

After lasering, all left to do was attach new wires. I did use a microscope for that. For scale, the wire running on top of the CPU has a 0.3mm diameter.

I ran some quick tests with the software to make sure the repair worked. Then a blob of hotmelt was applied to secure and protect the repaired pins:

HW-0.30-mini fixed

 

Backstory: I am also responsible for breaking the pins. I did solder the CPU at 31C3 without proper lighting using borrowed equipment. The temperature on the soldering iron was set to 450°C, I failed to check that. This lead to some major fuckup. Since I wanted to work with the board, the decision was made to simply cut of the broken pins. At the time I didnt need them.

15 thoughts on “Fix broken pins on QFP Package”

  1. This is awesome to a new level. Even after seeing the decapping of a blobbed chip in HaD, It never ocurred to me that you could also do this.
    My hat’s off to you!

  2. Man, that’s awesome repair work.
    I never thought of using a CO2 laser to remove the epoxy-mold/package to expose the leadframe.

    The only successful similar repair I made was using a micro-drill to drill down through the epoxy into the lead inside. Then ran a fluxed wire down into the hole. It drew the solder in to make the connection.
    Although my repair was a while back, before SMT components became common.

  3. A laser powerful enough to burn plastic, aimed at an area containing shiny metal surfaces… how were you watching / guiding the process?

    Did you watch via video camera, did you wear safety goggles – or did you just “eyeball” it and risk permanent damage from reflections?

    1. Alignment: I have visible alignment-lasers mounted to the nozzle. They arent that acurate (+-0.5mm), so I had an extra program to mark a spot on the IC. Then I moved the Chip accordingly.
      Protection: I closed the Lid of the laser-cutter, inspection & pictures were done inbetween passes.

  4. Hello,
    Nice result ! What’s the power of the laser ? Can you, please, tell us more about the laser settings (speed, power, number of pass, process duration, etc…)

    1. I used a noname chinese laser-cutter with 80W tube and 600x400mm working area.
      To remove the epoxy I used the engraving-function with 25% power and 200mm/sec speed. Each pass removed ~0.2mm of material.

      The whole removal-process including alignment took about 40minutes.

      @Alejandro: sorry, no video. Just the pictures in the blogpost above.

    1. @Jefry
      I did small passes, roughly 0.1 – 0.2mm on each engraving-pass. Inbetween, I did open the enclosure and did take a look ath the chip. Thats also how the pictures were made.
      As soon as the lead-frame was visible, I stopped lasering.

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