From an article:
Flux-induced corrosion (Copper Mirror Test)
A measure of the chemical corrosivity of a flux, the copper mirror test is referenced in a number of specifications (such as IPC-TM-650 Method 2.3.32), and is in common use as an indicator of the level of soluble ionic and aggressive activators in a flux. The test assesses the corrosion by cold flux (23°C) in a humid environment (50% RH) of a very thin film of copper on a glass slide: if there is significant corrosion, the film becomes transparent.
For liquid fluxes, the test involves placing two drops of a 35% solution of the flux on a 'copper mirror'. This is a glass microscope slide on which has been deposited approximately 30-50nm of copper, defined as a Cu thickness which allows the transmission 10±5% of normally incident 500nm wavelength light. Typically, a flux made of pure water-white gum rosin and isopropanol acts as a control, and a drop of it is also placed on the mirror. The mirror is then placed in a controlled environment of 23±2ºC and 50±5% relative humidity for 24 hours, rinsed in isopropanol and examined for any spots or areas where the copper has been removed by the flux.
The test has several drawbacks which have led critics to question its relevance.
The test indicates the potential corrosivity of the raw or unheated flux, which is not always indicative of the corrosivity of partially-heated flux (such as flux present on the component side of an assembly during wave soldering) or of fully heated flux (such as flux on the wiring side of a board)
The results can be difficult to interpret, being somewhat subjective and with no middle ground between pass or fail.
However, the test is quick and easy to perform, and its results correlate well with those of the more lengthy and involved surface insulation resistance test. It is widely accepted and is especially useful as a pre-screening test when testing a new formulation or as a routine incoming materials check.
In some versions of this test, it is applied to solder paste by first extracting any ionic species by boiling a sample of paste in solvent (propan-2-ol) and then concentrating the extract to approximately 35% solids by weight. It has been suggested, correctly, that this procedure is unfairly weighted against pastes with a low-solids flux content, so IPC-TM-650 Method 2.3.32 applies solder paste direct to the mirror.
ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: Wednesday, August 17, 2005 3:41 PM
To: [log in to unmask]
Subject: Re: [TN] Copper Mirror test for water-based fluxes
For those of us who only recently realized that something had to happen to a PCB before it was installed..(Assembly? What's that?)... be so kind as to tell us more about this test, and what it is supposed to tell you... and how to read it....
Any help is appreciated...(and needed)
Rudy Sedlak
RD Chemical Company
Bev Christian <[log in to unmask]> wrote:
It is such a long time that I have done one of these, that I don't remember what we did to evaporate the water! The alcohol based ones are easy, but the water ones?! Do you just let them set at room temperature or do you give them a little heat or what?
Bev
RIM
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