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SMT electronics assembly manufacturing forum.


Preheating a board with metalic coating on both sides

#20967

Preheating a board with metalic coating on both sides | 30 July, 2002

I am trying to get a profile on a thru-hole board with metalic coating on both sides. My preheaters are about maxed out and my profile is just reaching 200 degeres F. I'm not sure how much I can slow my conveyor down to get more heat. Does any one have any suggestions or data on how slow I can go with my dwell time. Thanks

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#20972

Preheating a board with metalic coating on both sides | 30 July, 2002

What's this 'metalic coating on both sides'? Is that like a 'two-sided board'?

I expect that your 200�F is the primary side temperature just prior to entering the wave. If not, you need more juice [depending on your flux and all that]. [Some modern wave soldering machines have two conveyors. The first runs sloooow for preheating and the second runs fast for soldering. Hot, eh? I gotta gimme wanna demm]

The optimum contact (dwell) time in the wave should be 2 seconds. Contact band width is a function of conveyor speed. The formula goes like this: t= d/v, where t = Dwell time of PCB in solder wave d = Geometrical length of contact between PCB & solder wave v = Conveyor speed

For an example, 5 cm of contact band width at 150 cm/min conveyor speed will give you 2 seconds of contact time and 2 cm of contact band width at 60 cm/min conveyor speed also delivers 2 seconds dwell (contact) time. [From a Sandia Laboratories chart]

I wonder if you couldn�t bake your boards prior to waving them as a way to put more energy into them.

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#20999

Preheating a board with metalic coating on both sides | 31 July, 2002

Dave, thanks for the reply. These boards have metal plating covering 99 percent of both primary and secondary surfaces. The only places without the metal plating are the extreme outer edges and about an 1/8 inch surrounding the plated holes.

We do prebake boards before flow, but I don't want them hot when I take a profile because I couldn't run them that way. We use a foam fluxor and the warm boards will kill the flux.

Your mention of running them slower over the preheater and then speeding it up over the flow is something I might try. That sounds like that would help from having a too- long dwell time over the pot. Thanks again

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#21005

Preheating a board with metalic coating on both sides | 31 July, 2002

Foam fluxer, ouch!! That hurts.

How about this? * Make a sheet metal box to cover your preheaters. [If your boss is really cheap, make a 'box' with 1/2" chicken wire and cover it with aluminum foil.] * Prebake the blank out of the boards, bag the foam, flux with a paint brush or a spritzer bottle, run the sukka. [Don't tell me. Yer running NC, eh. No, you can't be if yer foamin'. Yes!!! This'll work.]

Oh yeh, I almost forgot!!! I want the name of the looney-tones that designed this board!!! I'm gunna pimp slap the slobber out of him.

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#21021

Preheating a board with metalic coating on both sides | 1 August, 2002

Dave, I would have never thought of the sheet metal box.

My west coast contact, who has dealt with this type of board before, told me yesterday to go ahead and try it at this profile anyway, as the metal plating holds more heat. I was pleasantly suprised to see that the board flowed up fine at that low profile even though it is an extremely thick board.

By the by, I have three assemblies on this contract that are designed this way. My opinion of them is not to great either. Thanks again for the imput.

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