Wetting balance

The justification for the projected interface contribution is presented elsewhere [1-4]. The total force -fapp is that measured by a wetting balance [5]. 

The wetting balance technique is a variant of the maximum pull (or detachment) method used to measure liquid-vapour surface tensions (Keene 1993). It is nowadays widely employed in the electronics industry to quantify wetting of solders, but has also been used for wetting studies in metal/ceramic systems (Naidich and Chuvashov 1983b, Nakae et al. 1989, Rivollet et al. 1990). As compared to the sessile drop method which needs planar substrates, solids of various geometry can be studied by this technique. 

Table 3.3. Capillary properties of molten Sn/a-AhOj system measured by the wetting balance technique at 1370K using A12Oj cylinders (De Jonghe et al. 1990). fly is calculated by equation (3.22).

Table 3.4. Comparison of 0Y and

The adhesion tension, r, was measured with Guastalla s wetting balance [13]. This apparatus was designed according to Wilhelmy s principle [30] for measuring the surface tension of liquids. 

We have been able to define the difference in behavior of the mineral-hydrocarbon-water system according to whether the mineral is initially wetted by water or by hydrocarbon, by utilizing J. Guastalla s wetting balance which permits one to measure successively the immersion, and emersion, adhesion tensions. 

Guastalla Wetting Balance. This instrument [2,3] allows one to measure the force exerted on a vertical slide (2.5 x 2 cm.) when it is partially immersed in a liquid or, as in the case with which we are concerned, when it is placed perpendicular to the interface of two liquids, the upper part of the slide being in the lighter liquid and the lower part in the heavier one. 

Figure i. Guastalla s wetting balance Tracing of Wetting Cycle... 

Measurements of adhesion tensions on polished mineral slides by the Guastalla wetting balance point out certain aspects of the physical mechanism of the wetting of aggregates with doped hydrocarbons in the presence of water. 

Refer to Chap. 42 for detailed information on solderability of PCB surface finishes. Testing methods are contained in the comprehensive joint industry specification ANSI/IPC J-STD 003. Surface finishes are commonly tested in production at the board fabricator using a solder float or solder dip method. When qualifying the finish, an OEM or assembler uses more equipment-specific tests such as wetting balance, rotary dip, or paste spread methods. Solderability should be consistent from day to day and lot to lot, with very little degradation after exposure to at least three assembly thermal exposures. 

SOLDERABILITY INCOMING INSPECTION AND WETTING BALANCE TECHNIQUE... 

In both these specifications are test methods that are not approved for accept/reject criteria, but that produce data that is useful for process development, shows what really happens during the assembly process, and if tested correctly meets the most stringent of evaluations to modern measurement analysis.These are tests E, F, and G for the J-STD-002 and test F for the J-STD-003.The test protocol detailed in this chapter is designed to change the test status of the wetting balance to one capable of producing accept/reject data, and more importantly, to provide accurate data for process improvements. 

FIGURE 4Z3 Normalized data for one individual from a placing the test weights wetting balance lest the correct value is 0.98 mN. 

Wetting Balance Protocol to Meet the Requirements of an Acceptable GR R... 

What was needed was a test protocol that allowed the wetting balance to be used for what it was designed for measuring solderabUity. This required producing a test sample that is considered uniform and consistent, sample to sample. This known good coupon was created and subsequently a test protocol developed. This detailed test protocol maybe found in the Appendix sections of the ANSI-JSTD-002 and ANSI-JSTD-003 documents. 

Wetting Balance Protocol Development. This protocol was run using three types of wetting balance. To demonstrate the power of both the protocol and the wetting balance, three individuals were requested to run the test at every location an expert in wetting balance... 

FIGURE 42.4 An example of the consistency of wetting balance using the test protocol-ten individuals participated in the generation of the previous data. 

FIGURE 42.6 Possible outputs from a solderability test using a wetting balance. 

INTERPRETING THE RESULTS WETTING BALANCE SOLDERABILITY TESTING... 

TABLE 42.3 Comparison of the Power of a Wetting Balance Test to a Dip and Look Test for Process Development... 

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