hot air pencil not working

[zze110]

Hello,

I am trying to remove a surface mount 10/100 ethernet chip from a pcb and replace it.  I purchased one of the cheap ebay hot air pencils thinking the chip would fly right off the board.

However, I cannot even make the solder melt.  I can melt solder easily on the roll but nothing on the PCB.  I tried adding some solder to the chip leads and it applies immediately.  Once there it hardens and I am unable to melt it again!

I am thinking the board is sucking out all the heat I apply before the solder gets hot enough.  How can I keep this from happening and remove the part?  The chip is a 48-pin lqfp package.

Thank you.

[tautech]

Welcome to the forum.
You will need to add additional heat on the PCB.
Either a hot air gun or pre-heat in the oven and work quickly.

Some carefully cut the package leads and then de-solder each lead.
Be careful not to rip the pads up.

[divelectservices]

You need a preheater under the board.

[zze110]

Thank you, I will try to get one.

The board I am working with I believe was wave soldered.  I read that they use glue to adhere the chips to the board?  Would this cause an additional problem if true?

Thanks again!

[aargee]

Most likely unleaded solder. A real PITA as it doesn't often play well with leaded and has a higher melting point.

[Howardlong]

Be aware that if it's on a multilayer stack, melting solder is quite a bit harder than on a one or two layer board as the ground plane layer has a lot of thermal mass.

If the chip in question is a QFN oe other device that has a ground pad under the chip this makes the job harder too.

Is it a hot air pencil, or a hot air desoldering gun? A pencil will be useless for a chip bigger than about 4mm^2. A pencil looks like a normal sized soldering iron but with a small bore for the hot air, perhaps a couple of mm diameter bore and a shaft under about 1cm diameter. A hot air desildering gun has a shaft diameter of 2 or 3cm, and a bore in step with that, and should be able to completely cover the chip with heat without waving it around given the appropriate funnel tip (or occasionally no funnel tip at all for the bigger devices).

Make sure you have the air turned up enough, and there's enough temperature. Mine is at 320C. For multilayer boards with embedded ground planes it has to be within a couple of millimeters of the chip for about twenty seconds or so to shift it. You can see the solder melt on each pin under the microscope, and I prod the chip a little evey now and then with the tweezers until the ground pad melts too and the chip moves, then lift it off.