INFLUENCE OF HYDROSTATIC PRESSURE ON COMPONENTS 



M. FLA.TO 

 U. S. Naval Research Laboratory 

 Washington, D„ C. 



ABSTRACT 



After a cursory investigation into the effects 

 of high hydrostatic pressure upon components used 

 in electronic circuitry, a more thorough look has 

 been made in certain areas . Components which are 

 satisfactory for short term tests have succumbed 

 after longer periods under pressure. 



In the last reporting it was shown that a 

 test block of thin-walled aluminum cylinders 

 embedded in plastic withstood a short term test . 

 In the present test series the same block_-was 

 subjected to 6 months duration. One cylinder 

 failed and the second was reduced in diameter 

 along its length. This test indicates the "cold 

 flow" effect upon plastics which in turn can be 

 transmitted to components. 



The pressure tank used for these investiga- 

 tions has been modified to vary temperature as 

 well as pressure. It is capable of lowering tem- 

 perature to approximately C. 



LONG TERM PRESSURE TESTS 



it 



In the earlier report of pressure tests 

 was mentioned that a long term test was in 

 progress. This test was devised to determine the 

 thickness of potting material necessary to pro- 

 tect components such as transistors and capaci- 

 tors which have internal cavities and voids . 

 Fig. 1 shows k very thin walled aluminum tubes cast 



into a plastic block. The specimens were placed 

 at l/32 inch increments from the surface of the 

 block. The two closest to the surface (l/32 and 

 l/l6 inch from the surface) imploded at about 

 2,500 psig; the other two, more deeply embedded, 

 successfully withstood the full 10,000 psig pres- 

 sure. The end of the test block containing the 

 two tubes that had not been crushed in the origi- 

 nal pressure test was placed in a small pressure 

 tank where the pressure of 9? 000 psig was main- 

 tained for 6 months . 



The samples were removed from the tank at the 

 completion of the long term test and its condi- 

 tion was observed to be as shown in Fig. 2. The 

 most obvious change was the failure of the cylin- 

 der situated 3/32 inch from the surface. Con- 

 siderable damage occurred, however, at other 

 places in the sample. The remaining cylinder 

 (situated 1/8 inch from the surface) was reduced 

 in diameter over a portion of its length. In 

 addition, a depression immediately over the axis 

 of the cylinder had occurred and was measured to 

 be 0.025 inch deep (averaged). When the sample 

 was first removed from the tank a bubble noticed 

 prior to the long term test was almost invisible 

 and on the underside of the plastic casting was 

 a depression 0.046 inch deep. In the first few 

 hours after removal from the tank, the tiny bubble 

 increased in size and forced the oil out through 

 a crack in the plastic. The photograph shown in 

 Fig. 3 was taken 5 days after the test block was 

 removed from the pressure tank. 



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Fig. 1. Hollow aluminum cylinders in plastic and exposed to short term hydrostatic 

 pressure of 10,000 psig. 



Superior numbers refer to similarly numbered references at the end of this paper. 



169 



