STUDY OF FREE-RANGING SHARKS 



435 



These are several more or less standard methods for assembling modern 

 solid-state circuits. These are listed in order of increasing miniaturization. 



Discrete wiring— This is the "standard" method of circuit construc- 

 tion, in which the individual components are soldered together. Usually the 

 neatest results are those utilizing a printed circuit (PC) board, although the 

 most compact arrangements are sometimes those wired without such a board 

 (Figure 8). Most USTs in the past have been built this way, and for very 

 simple circuits there may be no significant size advantage in using a more 

 sophisticated method. 



Figure 8 Comparison of construction methods for CSULB Mark V transmitter circuits 

 (single channel). Left: Discrete wiring of the compact boardless type. Right: Thick-film 

 hybridization. The multipin hybrid contains most of the circuit components. The 

 remaining external components include the frequency crystal (TO-5 can at top), 

 capacitors, resistors, and a multipin connector. 



Thick-film hybridization— This type of miniaturized circuit construc- 

 tion allows a considerable size reduction over discrete wiring. The conductor 

 pattern is produced on a ceramic substrate by a "silk-screen" method, the 

 smallest conductor lines and spaces being about 0.25 mm wide. Miniature 

 components such as chip capacitors, integrated-circuit chips, other semi- 

 conductor dice, and external-connector pins are applied to the substrate. 

 Additional connections are made by hand under a binocular microscope 

 using 0.025-mm wire, usually attached using an ultrasonic or thermo- 

 compression wire-bonding machine. Resistors can be added as drops of resis- 

 tive ink and later trimmed to desired values using an abrasive airbrush. The 

 finished circuit is tested, then coated with a protective epoxy or otherwise 

 mounted. 



Since there is usually an initial setup fee, thick-film construction is gen- 

 erally not more economical than discrete wiring in quantities of fewer than 



