1. Field of the Invention
This invention relates in general to an apparatus for automatically placing and soldering very small electrical components onto a circuit board.
2. Description of the Prior Art
Many high frequency circuits require the use of very small, discrete electrical components. For example, a KA band millimeter wave radar transceiver commonly requires the use of microscopic gallium arsenide (GaAs) transceiver diodes. These transceiver diodes commonly have dimensions of only 0.008".times.0.008".times.0.0015". Two foil leads or "beam leads" are attached, giving the component an overall length of 0.025". The beam leads of the diodes must be soldered to the transceiver microstrip with an extremely high degree of accuracy with respect to the circuit artwork.
Automatic chip placing equipment capable of handling components of roughly the same size has been available for some time. These machines utilize miniature mechanical collets which act as fingers to square the chip as it is gripped. The component is then ejected from the collet by an ejection pin to a spot adhesive which holds the component in place on the circuit board.
Gallium arsenide is an extremely fragile substance, however. In the configuration of the beam leaded package, even slight mechanical contact to the body of the diode creates a serious risk of cracking or breaking the chip. Hence, the use of a mechanical collet would be unacceptable for handling the GaAs components in the assembly of the radar transceiver.
In many situations, the very small GaAs components could be bonded to a rigid ceramic substrate using thermal compression bonding. For KA band operation, however, a PTFE laminated substrate offers cost and performance advantages over ceramic substrates. PTFE laminated substrates comprise a relatively soft material, and hence, thermal compression bonding results in small depressions in the microstrip which adversely affect the performance of the transceiver.
As a consequence of the fragility of the GaAs diodes and the softness of the PTFE substrates, assembly of the transceivers has been performed by using a hand soldering iron with the assistance of a high power microscope. The minute components invariably shift position due, in part, to the surface tension created by the molten solder. Thus, the diode must be physically held in place by the technician using a toothpick or other pointed tool. This task is painstakingly tedious, the solder joints are not always reliable, and there is a risk of damage to the very expensive beam leaded components.
As a result, there is a need for an apparatus which is capable of automatically handling very small electrical components without damage thereto and for soldering the components to a circuit board.