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General question about reflow

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  • General question about reflow

    I have been practicing for a few hours every day on dead boards, removing and replacing QFNs

    I had settled on a general procedure and I was looking for guidance

    I am using a QUICK hot air station

    1)I start at a high temp 600-615C at 3-4 inches from the board at high flow rate (100 on the quick)
    do this for 1-2 minutes with flux applied
    2) move in to 2 inches,temp cut to 550, cut air flow to 50.any higher and risk for blowing other components away. I try to be at 90 degrees to the chip to
    with gentle swirling motion of the air
    3) tap with tweezers to check movement, at this point there is a narrow band of flux at the edges of the chip near the attachments

    4) move in very tight 1/2 inch for brief period on all sides of the chip
    - here I have run into trouble..I learned ..NEVER pull on the chip, if you do... its not ready to come off ( i ripped a pad clean off doing this)

    5) move off and away to 2 inches, then back down to 1/2 to 1/4 inch..in bursts of 5 seconds or so...
    6) gradually let the chip tell you when it it ready to come off

    If my technique is wrong, please tell me

    Like I said, practice is the only teacher I have right now.

    Its been frustrating.

  • #2
    600-615C is too hot!!!!!!!!!!!!

    I use 430C at 120C. 1-2 min is too long, you should have most everything pulled within 30 seconds.

    See this video. This is a extreme case. These chips are likely the hardest to remove on the board due to the heatsink. https://youtu.be/_QC_KcnPQmE?t=274

    Also quick doesn't go to 600C. You have a fake, which is probably why it takes 2 min to do this. Use 1 temp and 1 airflow. 430C and 120 lpm works great.

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