|Ask the Experts|
April 8, 2020
Reduced pH and Specific Gravity of Flux
If both the pH and specific gravity of the flux used in our wave soldering operation are reduced, what effects will we see in the wave soldering process?
|Expert Panel Responses|
Let's take specific gravity first... if it is low, that means that there is more solvent and less solids present (I'm assuming a solvent-based flux, not water-based). If that's the case, you may see reduced fluxing action, depending on how great a reduction in solids.
If the reduction is moderate, you may in fact see no detectable effect. How much dilution of the flux is required to show a process effect is dependent on a lot of variables,including the properties of the flux, the solderability of the boards, the process settings in the wave, among other things.
Now let's take the pH part of the question. When you say pH is reduced,I interpret this as there being a lower pH number, which actually means more acidity. That normally does not occur if the solids content is on the low side.I'd expect a slightly less acid pH (higher number).
pH is not a great indicator of flux performance in any case, because the flux is relatively weakly buffered and the pH can be affected by other things. A better way to measure the acid content is by a simple titration to determine the acid number. Your flux manufacturer should be able to guide you as to how to implement such a test.
By lowering the pH of the flux, it becomes more acidic and the same applies to changing the specific gravity. As the alcohol in the flux evaporates the flux gets more concentrated or stronger and more aggressive.
Both of these issues will create performance changes on the product if there are not cleaned of regardless of whether or not they were low solid content flux.
The effects seen on the wave solder process may be minimal but the flux residues remaining on the board will be more aggressive and this will need to be reviewed and analyzed. From an equipment perspective the stronger the flux or the lower the pH of the flux, may cause increased maintenance problems on the conveyor system, fixtures and the venting system.
Vice President, Technical Director
If the same flux is used, when both pH value and the specific gravity are reduced, it usually means the activator content is below the normal. You might see a degradation on the activity of the flux, which may cause bridging, icicling, skipping, and poor hole fill etc.
Director New Product Development
Metallic Resources, Inc
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