Two parameters examined in this test were the time for the wetting force to equal zero (t to F = 0) and the time for the wetting force to attain 67% of its maximum force (t to 2/3 Fmax). Characteristic wetting times for a particular material can be obtained from these two parameters. The t to F = 0 provides information about the surface characteristics of the terminal while t to 2/3 Fmax indicates the solderability of the basis material.
For a sample of terminals in each of the categories, both the mean and standard deviation were calculated. The mean provides information on the actual level of solderability, while the standard deviation indicates the uniformity of wetting. Table 1 shows the results in each of the categories of the experiment.
1. Mean and Standard Deviation for Each of the Categories of the Experiment.
Categories 1 through 5 demonstrate that the fluxing and tinning operation can reduce the wetting times of steam-aged components. The RMA flux used on the steam-aged terminal caused the wetting time to decrease almost to the same level as the RA and OA fluxes.
From the hypotheses testing, it was found that there was not enough data to determine if there was a difference in the time for the wetting force to equal zero (t to F = 0) between categories 1 and 2. Therefore, we cannot conclude that the RMA flux actually caused a significant difference in the initial wetting action. There was, however, a significant difference in the time for the wetting force to reach 67% of the maximum wetting force. There was a significant difference between the variances of both categories 1 and 2 for both the t to F = 0 and t to 2/3 Fmax. The RMA flux seems to have reduced some level of oxidation and corrosion from the steam-aging environment and caused the wetting to be more uniform. It did not, however, restore it to a level that would be acceptable in high-reliability soldering.
The quick extraction from the solder pot did not seem to improve the ability of the solder to wet to the terminals of the connector. The RA flux did make a significant difference in the first time-element (t to F = 0), however, in the second time-element (t to 2/3 Fmax) there was not enough data to make the same conclusion. The variances in the first time-element and second time-element seemed to have decreased, even though there was not enough data to statistically conclude this. The OA flux caused the wetting times to decrease as well, though there was not enough data to statistically conclude that there was a difference in the first time-element. However, the second time-element was different. These results seem to match the accepted theory that as a connector is steam aged, the oxidation/corrosion of the terminals will increase. RMA, RA and OA fluxes will typically not breakdown heavier oxides. The RA and OA fluxes did not restore the solderability of the connector terminals to an acceptable level. Additionally, the RA and OA fluxes have a disadvantage in that they can, if not removed completely, induce corrosion over the life of the connector.
The second connector was received before it had been exposed to a water vapor environment. Category 6 is the component as received and category 7 is after steam aging. The results of the wetting balance testing did not show a significant degradation of the solderability after the steam-aging process. In fact, on the first time-element, the wetting time decreased, thus showing a significant increase in solderability. This might have occurred because of an insufficient cleaning process before testing. The second time-element did show a slight increase in wetting time, but not a significant one.
The connector terminals on the second connector were fluxed using RMA, RA, and OA fluxes and then tinned in a 63-37 solder bath. By tinning the connector terminals before steam aging, both the first and second time-elements decreased by a significant amount. All of the fluxes used brought the level of solderability within an acceptable level after steam aging.
It was recommended that a tinning operation occur
after the plating process. It appeared as though the nickel plating did not
provide sufficient corrosion protection for the basis metal. The porosity of
the nickel plating caused oxide formations to occur on the basis metal from
environmental gases. It was also recommended that the plating process be
checked for inadequate cleaning of the terminals before plating, control of
the plating process itself, and insufficient rinsing and drying after