The effectiveness of this cleaning and washing process is evaluated using sample glass boards with stuck-on chips which are contaminated with soldering fluxes to a certain degree and in a certain composition. The boards then undergo a cleaning cycle along with boards fitted with printed circuits.

Due to the fact that chips are normally stuck onto the smooth surface of a glass board, in these tests they tend to become unstuck and fall off. This is undesirable – it means increased testing costs and lost time. This problem is resolved to some degree by etching the surface with hydrofluoric acid before the chips are stuck on; however, this is not an adequate solution since the board becomes opaque. Such opaque boards can no longer be evaluated optically.

A solution has now been provided by a method and device for surface treatment, developed at the Institute of Microelectronics (by Ing. Martin Buršík, Ing. Jaroslav Jankovský and Ing. Michal Řezníček). The method consists in a surface treatment in which an interlayer of glass paste is applied before the chip is stuck on. Before it has had a chance to dry, the layer is powdered with a special dust of heat-resistant material using a spraying device. Drying and firing at a high temperature follow, during which the dust is trapped on the required parts, where it forms an opaque surface. Residual non-trapped dust is washed off, so that mechanical cleaning does not cause the surface to frost up and thus prevent optical testing.

This method and device will guarantee up to ten times better adhesion for chips stuck onto the testing substrate, and thus allows tests to be repeated several times, which means both financial and time savings.

Both the method and device are protected:

• by a patent: “Method of Forming an Interlayer on Glass Testing Substrates Intended for Affixing Chips, and a Spraying Device for Realization of the Method”;
• by a utility model: “Device for Spraying an Interlayer onto Glass Testing Substrates Intended for Affixing Chips”.
• a European patent application has also been filed.

Source of figure and photo: Institute of Microelectronics, Faculty of Electrical Engineering and Communication Technologies BUT