| Anyone using hot air nife for wave soldering process. | Does it work? | Does it really eliminate solder bridging and does it create any other problems? | | any feed back will be much appriciated. | | Thanks | | Tony A | | Tony,
The hot knife is a great invention. It opens up the window for both the process and the design. Now, in a perfect world, board designs would not violate keepout zones between pads & pads and pads & vias, nor would the leads be closer than 100 mil centers, the leads would be trimmed to the perfect length, and SOIC's would have theive pads on all trailing sides. By the same token, all operators would be conscientious enough to set perfect wave heights and maintain proper nozzle setups to get perfect peel offs. And all fluxes would have powerful surfactants and high thermal stability to act like the 310B and help eliminate bridges before they form.
Reality Check! Designs aren't perfect, neither are the humans, and very often we have to work with what we are given. WHich brings me to the hot air knife. It is the great forgiver. It "blows away" those design issues, and if you're wave setup ain't quite optimal, you're covered there, too.
It's a powerful tool. But if you don't use it right, it can get you into lots of trouble by blowing solder into places you don't want it to go - like up through holes and onto the top of the board, all over the inside of the machine, or out the load end onto operators.
My best results with the hot knife are running it at high temperatures and low pressures. The high temp (set at 800 F at the heater, about 650F at the delivery to the board) keeps the solder warm and at low viscosity while the pressure breaks the bridges. The low pressure (aroud 5 psi) means a low velocity of the air (or nitrogen) stream, which successfully debridges without making a mess of things.
One note on the knife - in inerted systems like the Electrovert contour, the knife entrains a good amount of air, and your soldering atmosphere's purity can decrease to only 95% nitrogen. This means more dross, but studies I've done show no sizable impacts on solderability or joint quality.
I'll post a Nepcon paper to the library on the effects of the hot knife on the soldering environment.
Chrys
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