United States Patent Number 5,789,068
August 4, 1998
The invention provides a solder preform coated with a predetermined thickness of parylene which physically and chemically protects the preform, as well as a provides a unique optical interference coating which reflects at characteristic frequencies. When predetermined thicknesses of parylene are selected, the parylene coating provides an interference coating which causes the solder preforms to appear green, or gold, or blue in color. The parylene coating, which is otherwise colorless and transparent thus enables solder preforms to be visually distinguishable by alloy type (or customer) by the use of colors, or blends of colors. The invention further provides an effective method of visually verifying the reflow status of a solder preform during manufacturing by examining the color of the solder preform after heating. The interference colors provided by the parylene coating do not persist through the reflow process, and thus, the change in color of the solder preform after reflow can be used as an effective visual check to determine if the preform has been heated sufficiently.
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