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Trapped Flux Under Component

Greg H

#8420

Trapped Flux Under Component | 28 November, 1999

What are the possible consequences when there's a flux entrapment (location: vias under components)under components during wave soldering?

thanks

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#8421

Re: Trapped Flux Under Component | 30 November, 1999

Greg: It depends on the specifics of the flux you are using. You didn�t say. Generally, using a:

� "No-clean flux" should create no flux entrapment problems for most applications. � RMA with 25% or more solids as a "no-clean" should create no flux entrapment problems for most applications. � Water soluble fluxes and many of the RMA/RA fluxes with medium and high activity levels could create flux entrapment problems for some applications.

There�s a wide range of possible consequences of flux entrapment when using water soluble fluxes and many of the RMA/RA fluxes with medium and high activity levels. For instance:

� Nothing, because you�ve done a great job of cleaning the board. � Nothing, because you�ve got a great solder mask. � � � � � Flux residue coats the via, is not washed away, reacts with metal surfaces, and causes a failure. The failure causes the airplane crashes over a large metropolitan area and kills thousands of innocents. Then, they make you watch the "Tractor Pull Channel" on cable all day long.

You didn�t say if these were primary or secondary side components. For primary side components: Consider that in addition to piping flux up and under the component, the via could act like a heat pipe during wave soldering. The spot heating could damage the component.

I suggest that you:

1 Get your designer to move the via. Big deal!!! 2 Get your board fabricator to plug vias. 3 Do some laboratory work and evaluate the residues left in the via. 4 Do some laboratory work and evaluate the heating effect on the component.

My2�

Dave F

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