POINT-CONTACT TRANSISTOR SURFACE EFFECTS 



799 



Table VII 



Treatment 



None 



ZnCl2-NH4Cl Flux 

 Flux and heat .... 



Ave. No. of 

 Pulses to Form 



2 

 3 



7 



Average 

 /c(6, -5) 



-13.8 ma 



-13.5 



-10.4 



Average 

 /c(0, -20) 



-1.7 ma 



-1.8 

 -6.0 



Fig. of Merit 

 /c(6, -5)/ 

 IciO, -20) 



8.1 

 7.5 

 1.7 



in the attainable average alpha has oeciirred even though the forming 

 objective was the same. Finally, the curve denoted "unit" represents 

 data on the first four completed units out of the same group from which 

 the manipulator and header samples were taken, A slight decrease in 

 average alpha is ol^serA^d at this point. However, previous experience 

 has indicated that this is an expected effect caused by the addition of the 

 impregnant. This chart suggests that the point soldering operation in 

 the process is causing a significant degradation in the formability of 

 transistors passing through this step.* 



This process step consists of placing the germanium wafer, which has 

 already been etched and mounted on the header, in a point alignment 

 tool. The point spacing and force is adjusted and the points are then 

 soldered to the header point-wire support. In the early stages of this 

 process a corrosive zinc chloride-ammonium chloride solder flux was 

 necessary to obtain efficient soldering. The effect of this solder flux on 

 the formability of micromanipulator transistors made on such surfaces 

 is shown in Table VII. These units were formed to the acceptance cri- 

 terion of Vc(S, —5.5) ^ 2.0 volts. Each figure represents the average 

 of ten imits treated in the same way. 



The value of the use of a figure of merit such as suggested earlier is 

 illustrated in this table. Since the average alpha (denoted here by 

 /c(6, —5) is related to the forming objective, one might presumably 

 keep forming until the average alpha was the same as for an easily formed 

 transistor. In this case Ico tends to increase. Under these conditions, if 

 one examined only average alpha, the data might easily be misleading. 

 From an examination of the figures of merit in Table VII one concludes 

 that the corrosive flux plus a heating cycle tends to degrade the ger- 

 manium surface to such an extent that transistors are formed only with 

 great difficulty. 



The finiction of a flux during the soldering process is to remove any 



* Curves of this nature have also been obtained by N. P. Burcham in in- 

 vestigation of soldering flux effects in hermetically sealed point contact transis- 

 tor processes. 



