Research On The Processing Characteristics And Servo Control Strategy In Semiconductor WEDM

As demand for semiconductor in science and technology areas increases, scientific researchers putforward higher requirements for semiconductor materials processing. Because of its no macromachining force character, electrical discharge maching (EDM) technology is very suitable for theprocessing of brittle semiconductor materials. After many years of hard work, researchers alreadyhave a certain understanding for the mechanism, features and process of semiconductor EDM,forming a relatively complete theoretical system and parameters data base. A certain range ofresistivity of semiconductor can be processed now. At present the biggest technical problem insemiconductor EDM processing is automatic servo control. The existing EDM servo control systemsare all based on the maching of metal materials. When they are used in semiconductor materialprocessing, there are significant limitations. These servo control systems can’t accurate judge theno-load, normal processing and the short circuit state, leading to be unable to control the servo feed.Through researching the current and voltage characteristics in the semiconductor wire cut electricaldischarge machining (WEDM), this paper puts forward a new kind of WEDM servo control strategybased on current pulse probability detection and develops a new servo control system. Based on thenew servo control system, the corresponding system parameters and processing parameters wereresearched, finally realizing the high efficiency, precision and stability cutting of semiconductormaterials. Specific works are as follows:（1）The current and voltage characteristics of semiconductor WEDM were studied.And based onthese characteristics, failure reasons of existing EDM servo systems in semiconductor materialprocessing were analyzed. The climb type current phenomenon in semiconductor WEDM is analyzed.The reasons and influence of the electric current parameters on the climbing properties were alsostudied. In this paper the mechanism of small holes phenomenon on semiconductor material surfaceafter WEDM was studied and its influence on the heat transfer process in the machining wasanalyzed.（2） According to the different current and voltage characteristics between no-load, normalprocessing and short circuit conditions, two feasible servo control methods were proposed, namely thedelay breakdown time control and current pulse probability detection control. Through thecomparison of the advantages and disadvantages of the two methods, we chose the current pulseprobability detection method.（3） The relationship between current pulse probability and feed speed in semiconductor material WEDM were studied. And a new semiconductor WEDM servo system was developed based on thecurrent pulse probability. The related system parameters were researched and optimizated, providing abasis for the selection of system parameters.（4） The micro contact discharge phenomenon in semiconductor material WEDM and its reasonswere analyzed and discussed. The cutting efficiency on the micro contact condition was studied, andthe mechanism of cutting efficiency greatly improved than normal processing was analyzed.（5） By processing the small, complex and variable thickness pieces, the system performance wasverified. Finally the high efficiency, precision and stability maching of semiconductor by WEDM isrealized.