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Soldering is now lead-free. Reflow soldering quality with solder paste can be maintained by controlling the furnace temperature or determining the temperature profile on condition that the solder paste material is decided and the materials, surface treatment, or surface conditions during storage of parts and PCB patterns are kept clean. In the case of dip soldering, on the other hand, work is sequentially flown into molten solder, so that copper as a PCB pattern material and palladium, silver lead, and other various components employed for the surface treatment of part leads melt into solder to cause the solder composition to change.      If lead and bismuth are molten into solder, the melting start temperature of solder lowers rapidly. Extremely speaking, solder does not become solid easily to cause a soldering failure. Since the component ratio of copper and tin changes unavoidably, it must be monitored by a certain method. Periodical analysis is desirable. However, X-ray fluorescent analysis, atomic absorption spectrophotometry, and chemical analysis are time-consuming and expensive. They are also difficult as a control method in a factory. Due to these circumstances, we offer a method of measuring a component change of these materials at soldering site. FEATURES & BENEFITS Pb measurement range: 0 - 0.2% accuracy: +/- 0.015% Cu Measurement range: 0.3 - 0.9% accuracy: +/- 0.1% Easy test lead contents (%) of solder pot at production site Quick testing (about 40 minutes) Small sample (0.5oz) Low Cost Computer control, software data collection Table top model

MEASURING PRINCIPLE

      A sample heating curve is obtained by heating solder of a fixed quantity at a fixed heating rate, and a change from the first input solder composition is analyzed from the factors appearing in the curve in Figure 2.

      These elements are different from normal melting start temperature and solidification start temperature due to the influences of the sample quantity, heating rate, sensor sensitivity, and other factors, but the concept is the same. Since the instrument is used on-site, the heating speed is designed to be high for short-time measurement in large quantities (to a certain extent), and the sensor is designed to be durable at the sacrifice of its sensitivity.

      The solidification start temperature is normally obtained from a cooling curve, but we obtain it from a heating curve. It is also presumable that the primary phase solution cannot be picked up.

      A temperature sensor is mounted at the center of the sample pot. The most characteristic elements are selected and judged assuming that the solidification of a high melting substance occurs, from the outer edges due to gradual external cooling; and the solidification of a low melting point substance occurs finally at the center sensor.

MEASURING EXAMPLES

      3-1 A change of silver in tin-silver-copper system solder
      3-2 Mixing of lead in tin-silver-copper system solder
      3-3 Mixing of lead in tin-copper system solder

MEASURING LEAD DEVICE

      A measuring lead device has been made by taking notice only mixing of lead, which bases on the result of the experiment that mixing lead derive the curve. (ref. Figure 3.) It will be possible to make measuring instruments for observing a change of mixing copper and silver.

      The materials employed as samples in the said measuring examples were produced in small quantities by a solder maker according to our request. Data was prepared by cutting a small sample. section from of these materials in a solid condition. It is questionable whether the analytical values in the course of melting are equal to the samples component ratios. Data will be stored on continuous component change for future results.