Photocircuits Corporation

Louis J Stans

Thomas S Kohm

Christopher F Lynch

James Tullo

A dual air knife assembly for removing excess solder and leveling any remaining solder on a passing circuit board with a gas from a gas source in accordance with the present invention includes a first and second air knife. The first air knife has a first passage with a first inlet adapted to connect to the gas source and a first outlet adapted to be positioned adjacent the passing circuit board. The second air knife has a second passage with a second inlet connected to the gas source and a second outlet adapted to be positioned adjacent the passing circuit board. The first air knife is adapted to be positioned substantially perpendicular to the circuit board and the second air knife is adapted to be positioned at an angle less than 90 degrees and preferably between 20 and 60 degrees to the circuit board. The dual air knife assembly may include a spacer which separates the a first and second air knife and is recessed from the outlets of the a first and second air knife to create an expansion chamber. The distance the first and second outlets are from the passing circuit board and the temperature and pressure of the gas exiting from the a first and second air knife should all be substantially the same. Typically, the dual air knife assembly is used in a soldering system which includes a conveyor, a flux station, and a solder station. The dual air knife assembly is used in a process referred to as 'hot air solder levelling' to remove excess solder and more evenly distribute any remaining solder. A pair of dual air knife assemblies may be used in another soldering system where excess solder is removed and any remaining solder is levelled on both sides of a circuit board.

Dual air knife for hot air solder levelling

The apparatus and method operate by first generating a set of amplitudes for a constant current pulse. Each amplitude in the set is associated with one conductor on the reference printed circuit board and represents the amplitude which generates a determined voltage rise in that one conductor that is within a set range of a desired voltage rise for that one conductor. Each determined voltage rise representing the difference between a first voltage drop reading and a subsequent voltage drop reading taken across each conductor while the constant current pulse is applied. Once the set of amplitudes is generated, the apparatus and method generate a set of test voltage rises. Each test voltage rise is associated with one conductor on the test printed circuit board and represents the difference between the first and the subsequent voltage drop readings taken across that one conductor when the constant current pulse with the amplitude from the set of amplitudes for the corresponding conductor on the reference printed circuit board is applied to that one conductor. Once the test voltage rises are generated, then the apparatus and method compare the test voltage rise for each conductor on the test printed circuit board against the desired voltage rise for the corresponding conductor on the reference printed circuit board to determine if the test voltage rise exceeds the desired voltage rise. If the test voltage rise exceeds the desired voltage rise, then the apparatus and method identity the conductor as defective. The test apparatus and method may multiply each reference voltage rise in the set of reference voltage rises by a set factor to establish a table of adjusted reference voltage rises and then use the adjusted set of reference voltage rises when comparing and evaluating the test voltage rises.

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Setauket, NY, United States of America

Louis J Stans