Hey, if you came from a direct link, be sure to check out part 2: Installing a Socket on this PCB
Since it’s a Friday and we’re all taking it easy for a change, we’ll take this time to talk a little bit about using an off-the-shelf heatgun to work with SMT devices. I know this is a topic that’s been covered before on the web, but usually the instructions given are something like: “Just use a heat gun, dude”. A little light on the details, to say the least.
We’re here to tell you that it works. Very well actually, and we’re proud to say that when we’re evaluating a new IC this technique is essential. Perhaps you’re abusive and tend to kill a lot of chips, or perhaps you just want to see the statistical variation in 10 or 20 IC’s – you’re going to be doing a lot of chip removal and resoldering.
Trying to do it with a soldering iron may work for something like an SO-8, but if you start talking about >16 pins or any type of quad package – forget it! The extended heat you put on the board will burn the PCB and even worse – cause the traces to peel, ruining that board! So if you don’t want to build 20 boards for 20 IC’s, you need a simple and fast method that does not damage the PCB.
Now it doesn’t matter much WHICH heat gun you use, although it should be able to produce a good bit of air at >300C. In our experience, long heating times due to using a weaker gun are the biggest cause of PCB burn, bulge, or trace peel. Your mileage may vary, but we prefer to use both the highest air and highest heat setting in order to melt the solder on our target device in the shortest time – lowering the chance that the solder on the neighboring device has also melted.
A drawback of high air setting is the risk of blowing neighboring devices (usually tiny SMT resistors or capacitors) off their pads and maybe even off the board! You will need to weigh the risk at rework time and choose your airflow accordingly – if you have a device that’s simply SURROUNDED by tiny SMT caps, you may want to use lower air or make a foil cone for your heatgun to contain the hot air to the desired area. Here’s the heat gun we used here, peak temp is about 550C.
There’s really nothing magic about this heat gun – we’ve used any old gun the lab had on hand: Some piece of junk Sears gun, a paint removal gun, chinese no-names. It’s more the strategy of getting in, liquifying the solder on the component you want while minimizing the effect on nearby components, and getting the target component out. You’ll need a pair of tweezers in addition to the heat gun, unless your fingers are really strong. Kidding, kidding – get the tweezers.
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