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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Jeanjean

#9440

When usingnoclean flux or clean flux process? | 21 September, 1999

Dear All,

In order to understand the soldering technologies in SMT, I'd like to understand why some cards are soldered and then cleaned, or only soldered whitout water cleaning nor "ultra sound" wavelength.

I mean that I wonder why we use toxic flux if we do not need them. It's useless to waste our environnement with pollution when we can afford an other safer solution.

Thanks for your help. Jeanjean.

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#9441

Re: When using noclean flux or clean flux process? | 21 September, 1999

| Dear All, | | In order to understand the soldering technologies in SMT, I'd like to understand why some cards are soldered and then cleaned, or only soldered whitout water cleaning nor "ultra sound" wavelength. | | I mean that I wonder why we use toxic flux if we do not need them. It's useless to waste our environnement with pollution when we can afford an other safer solution. | | Thanks for your help. | Jeanjean. | | Dear All, | | In order to understand the soldering technologies in SMT, I'd like to understand why some cards are soldered and then cleaned, or only soldered whitout water cleaning nor "ultra sound" wavelength. | | I mean that I wonder why we use toxic flux if we do not need them. It's useless to waste our environnement with pollution when we can afford an other safer solution. | | Thanks for your help. | Jeanjean. | Jeanjean: Let's be clear:

� You should not breathe the residues of either washable or no-clean fluxes. Both can cause respiratory problems. � Flux is a chemically-active compound which, when heated, removes minor surface oxidation, minimizes oxidation of the basis metal, and promotes the formation of an intermetallic layer between solder and basis metal. � Low residue fluxes usually have lower solids content (less than 5%) than high-solids rosin fluxes. Their primary activator materials are weak organic acids (adipic or succinic acid). No clean residues are benign on a board surface and act as electrical insulators. � Organic acid fluxes have active ingredients such as organic hydrohalides, amines, and amides. These fluxes are water soluble since they contain no rosin. Good cleaning is critical with these flux types since their residues are corrosive and electrically conductive.

You're correct that cleaning flux from boards adds cost and loads the environment, but "no-clean" fluxes are not really clean. They leave a goop on the board. This creates several potential problems:

� In some applications, like high frequncy, the no-clean flux residues can interact with circuit functions. � No-clean flux residues can interfer with automatic test probes. � Some people don't like the appearance of flux residues. � Conformal coating of boards with no-clean residues requires more care.

Further, no-clean fluxes have a narrower soldering process window than washable fluxes, increasing the cost of soldering and material control. Continuing, the conversion from washable fluxes to no-clean fluxes is not always transparent. So, some product managers just don't want to pay for the transition.

Finally, cleaning processes can use recyclable materials that put a small load on the environment.

Good question

Dave F

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Brian

#9442

Re: When using noclean flux or clean flux process? | 22 September, 1999

| | Dear All, | | | | In order to understand the soldering technologies in SMT, I'd like to understand why some cards are soldered and then cleaned, or only soldered whitout water cleaning nor "ultra sound" wavelength. | | | | I mean that I wonder why we use toxic flux if we do not need them. It's useless to waste our environnement with pollution when we can afford an other safer solution. | | | | Thanks for your help. | | Jeanjean. | | | | Dear All, | | | | In order to understand the soldering technologies in SMT, I'd like to understand why some cards are soldered and then cleaned, or only soldered whitout water cleaning nor "ultra sound" wavelength. | | | | I mean that I wonder why we use toxic flux if we do not need them. It's useless to waste our environnement with pollution when we can afford an other safer solution. | | | | Thanks for your help. | | Jeanjean. | | | Jeanjean: Let's be clear: | | � You should not breathe the residues of either washable or no-clean fluxes. Both can cause respiratory problems. | � Flux is a chemically-active compound which, when heated, removes minor surface oxidation, minimizes oxidation of the basis metal, and promotes the formation of an intermetallic layer between solder and basis metal. | � Low residue fluxes usually have lower solids content (less than 5%) than high-solids rosin fluxes. Their primary activator materials are weak organic acids (adipic or succinic acid). No clean residues are benign on a board surface and act as electrical insulators. | � Organic acid fluxes have active ingredients such as organic hydrohalides, amines, and amides. These fluxes are water soluble since they contain no rosin. Good cleaning is critical with these flux types since their residues are corrosive and electrically conductive. | | You're correct that cleaning flux from boards adds cost and loads the environment, but "no-clean" fluxes are not really clean. They leave a goop on the board. This creates several potential problems: | | � In some applications, like high frequncy, the no-clean flux residues can interact with circuit functions. | � No-clean flux residues can interfer with automatic test probes. | � Some people don't like the appearance of flux residues. | � Conformal coating of boards with no-clean residues requires more care. | | Further, no-clean fluxes have a narrower soldering process window than washable fluxes, increasing the cost of soldering and material control. Continuing, the conversion from washable fluxes to no-clean fluxes is not always transparent. So, some product managers just don't want to pay for the transition. | | Finally, cleaning processes can use recyclable materials that put a small load on the environment. | | Good question | | Dave F | Dave is perfectly right. I would add one important rider: "no-clean", offering less good soldering qualities, has a corollary of economic and reliability importance. You can expect to have to retouch many more solder joints with it. This may be costly, especially if the components are not perfectly solderable.

I would add that ALL fluxes, without exception, produce something bad for the environment and "no-clean" ones are all VOCs at soldering temperature (the only difference is that they do not use an alcohol as a solvent). Furthermore, the residues of "no-clean" very slowly sublimate, emitting WOAs for years after the soldering process. Greenpeace and co. have not yet cottoned onto this :-)

Of all processes involving cleaning, water-soluble is the least nocive to the environment, offers the best soldering quality and is the most economic (see the UNEP Solvents Committee report 1998, chapter 2).

The link below and many other pages on the same site will give you much information on the subject.

Hope this helps.

Brian

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