Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


IR /Convection Preheats

Bill Copperthwaite

#13029

IR /Convection Preheats | 11 January, 1999

I have an Electrovert UPK 660c fitted with IR preheats top and bottom. We assemble a large range of multilayer backplanes and I was wondering if there are any advantages in changing to convection preheats.Has anybody got any views on the subject.

reply »

Chrys

#13030

Re: IR /Convection Preheats | 11 January, 1999

| I have an Electrovert UPK 660c fitted with IR preheats top and bottom. We assemble a large range of multilayer backplanes and I was wondering if there are any advantages in changing to convection preheats.Has anybody got any views on the subject. | Convection preheats kick butt on IR, especially in applications where there are large, heat-sucking ground planes.

The main benefit of convection is the more efficient heat transfer. The same assemblies that ran on our UPK with 850 and 900 degree preheat temps are now running with 270-300 degree convection temps.

You can cut down your recipe list with convection - the more efficient transfer allows you to run more assemblies under one recipe. I've got 107 assemblies and five recipes. 90% of the boards run on one of three main recipes.

You can get good topside wetting on holes tied to ground planes, too. I stuck a thermocouple in one of these holes when I was first looking at convection years ago. Whereas the heat from the IR will climb up the hole and out into the groundplane, the forced hot air gets the heat all the way to the top of the barrel.

It's a lot easier to use VOC-free flux with convection, as well. The air movement helps to evaporate the water carrier.

Guess I'm pretty biased, huh?

Chrys

reply »

Earl Moon

#13031

Re: IR /Convection Preheats | 12 January, 1999

| | I have an Electrovert UPK 660c fitted with IR preheats top and bottom. We assemble a large range of multilayer backplanes and I was wondering if there are any advantages in changing to convection preheats.Has anybody got any views on the subject. | | | Convection preheats kick butt on IR, especially in applications where there are large, heat-sucking ground planes. | | The main benefit of convection is the more efficient heat transfer. The same assemblies that ran on our UPK with 850 and 900 degree preheat temps are now running with 270-300 degree convection temps. | | You can cut down your recipe list with convection - the more efficient transfer allows you to run more assemblies under one recipe. I've got 107 assemblies and five recipes. 90% of the boards run on one of three main recipes. | | You can get good topside wetting on holes tied to ground planes, too. I stuck a thermocouple in one of these holes when I was first looking at convection years ago. Whereas the heat from the IR will climb up the hole and out into the groundplane, the forced hot air gets the heat all the way to the top of the barrel. | | It's a lot easier to use VOC-free flux with convection, as well. The air movement helps to evaporate the water carrier. | | Guess I'm pretty biased, huh? | | Chrys | | I certainly agree with Chrys about most everything. Who wouldn't?

Another of the primary reasons to get rid of IR is it blows stuff to bits. Focused IR got it's start, as did I, in the 60's. It was used then for co-firing hybrid thick film circuits. Still is as ceramic isn't harmed by it.

You should have been around in the 70's when bare fab shops started employing it to fuse tin/lead plated solder. Amazing how multilayer boards delaminate and fly apart during the process.

In the 80's, people began using IR/Convection processing to get away from focused IR reflow. The primary reason was IR likes dark objects like components. It likes to heat and eat them thereby destroying some and prevening what is sought - solder wetting and acceptalbe solder joints.

Then along came Steve Dow and hot air convection reflow and no more problems?

Earl Moon

reply »

Fluid Dispense Pump Integration

PCB Rework / Repair Services