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  • Author Author: baldengineer
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I need your ideas on how to test flux!

baldengineer

Bucket of Flux Paste

I have been thinking about an episode that compares different types of flux. Primarily I want to compare rosen, water-soluble, and no clean.

I need your help with at least two aspects.

First, what to cover. The two key areas I am thinking about are how effective are each and how difficult are they to clean? Are there any other areas we should explore?

Second, how to do the testing. My thought was to sand the finish off some scrap PCBs and expose them to moisture to generate some corrosion. Is there another way to simulate joints that require cleaning? Maybe an additional test needs to be soldering new components/PCBs for comparison?

Ultimately, I can solder parts to those PCBs and then compare the resulting solder joints with a microscope.

I'm open to the community's thoughts on what to test and how. So let me know what you think!

  • in reply to baldengineer

    yes. For solder paste, you have to purchase a different item for lead-free vs leaded applications. Because the viscosity at the solder temperature has to be optimal.
    If you use for-leaded paste in lead-free work, it is way to fluid at the temperatures used.
    If you use for-lead-free in leaded work, it isn't fluid enough.


    These pastes have - on purpose - a narrow temperature range of application. If they would have a broader range, physical symptoms would occur at the wrong time and components would either flow away or not center at the right moment.

  • in reply to DAB

    Another great point/idea! Temperature. Thanks @DAB.

  • You could look at the different types of metals that each type of flux can clean.

    You could also look at the temperatures at which the flux actually need to attain before it supports the soldering.

    Something like the rule of thumb for plumbing flux, where you wait until the flux bubbles before you apply the solder.

  • in reply to michaelkellett

    > "I don't think there is much point in testing flux on deliberately chosen bad parts"

    The purpose is to show extremes.

  • I don't think there is much point in testing flux on deliberately chosen bad parts  - the solution to that problem is not to use bad parts !

    On the other hand testing on a nice new gold plated pcb maybe gives the flux little chance to show its goodness.

    So I suggest hand soldering 0603 surface mount caps and resistors and TQFP packages (by "drag" soldering) on new but cheap solder levelled or immersion silver coated boards.

    I use very runny (like water) flux applied with a paint brush. (Warburtons Future 315). It's sold as no clean but I almost always clean using Safewash (water soluble soap) in an ultrasonic cleaner and rinse with tap and then 2 flushes of de-ionised water.

    For re-work I might just use IPA as Shabaz suggests.

    I've had Doug's problem with residues being OK until they absorb moisture.

    MK