Monitoring gas leakage rates from hermetically sealed devices
A method for monitoring a gas leakage rate from a hermetically sealed device, such as a hermetically sealed data storage device with an interior helium atmosphere. In some embodiments, a diffusion rate of inert gas from a hermetically sealed first device is monitored until steady state diffusion is reached, and a standard time constant for the first device is identified. Next, the diffusion rate is monitored for a second sealed device for a portion of the time required for the first device to achieve steady state diffusion, and the time required for the second device to reach steady state diffusion using the standard time constant is calculated.
1. A method comprising:
monitoring a diffusion rate of inert gas that diffuses from a hermetically sealed first device and through an inert gas permeable membrane adjacent the first device until a steady state diffusion rate is achieved;
identifying a standard time constant for the first device to reach the steady state diffusion rate;
monitoring a diffusion rate of inert gas that diffuses from a hermetically sealed second device and through an inert gas permeable membrane adjacent the second device for a portion of the time required for the first device to achieve the steady state diffusion rate; and
calculating the time required for the second device to reach steady state diffusion using the standard time constant.
2. The method of claim 1 wherein the inert gas is helium.
3. The method of claim 1 wherein the first and second devices are data storage devices.
4. The method of claim 1 further comprising the step of monitoring the ambient pressure of the first and second devices.
5. The method of claim 1 wherein the monitoring step for the first device comprises:
maintaining the first device at atmospheric pressure on one side of an inert gas permeable membrane; and
subjecting the opposing side of the membrane to a vacuum.
6. The method of claim 5 wherein the monitoring step for the second device comprises:
maintaining the first device at atmospheric pressure on the one side of the membrane; and
subjecting the opposing side of the membrane to a vacuum.
7. The method of claim 6 wherein the monitoring steps comprises:
measuring the diffused inert gas with a mass spectrometer.
8. A method for determining gas leakage from a hermetically sealed device with an inert gas atmosphere, comprising:
(a) placing a first sealed device in a diffusion chamber having a gas permeable membrane;
(b) creating a negative pressure across the membrane to effect gas diffusion there through from the first sealed device;
(c) monitoring the gas diffusion from the first sealed device and determining the time constant for the first sealed device to reach steady state diffusion;
(d) placing a second sealed device in the diffusion chamber;
(e) creating a negative pressure across the membrane to effect gas diffusion there through from the second sealed device;
(f) monitoring the gas diffusion from the second sealed device for a pre-determined portion of the time required in step (c); and
(g) calculating the time required for the second sealed device to achieve steady state diffusion using the time constant.
9. The method of claim 8 comprising minimizing the volume of atmospheric air surrounding the first and second sealed devices.
10. The method of claim 8 wherein the inert gas is helium.
11. The method of claim 8 wherein the first and second sealed devices are hard disc drives.
12. The method of claim 8 further comprising the step of monitoring the ambient pressure of the first and second sealed devices.
13. The method of claim 8 wherein the monitoring step for the first sealed device comprises:
maintaining the diffusion chamber substantially at atmospheric pressure on one side of an inert gas permeable membrane; and
subjecting the opposing side of the membrane to a vacuum.
14. The method of claim 13 wherein the monitoring step for the second sealed device comprises:
maintaining the diffusion chamber at atmospheric pressure on the one side of the membrane; and
subjecting the opposing side of the membrane to a vacuum.
15. The method of claim 14 wherein each of the monitoring steps comprises:
measuring the diffused inert gas with a mass spectrometer.
16. A method for measuring the gas diffusion rate of a hermetically sealed device having an inert gas atmosphere, comprising:
(a) providing a test chamber including an upper diffusion chamber and a lower vacuum chamber;
(b) placing a first hermetically sealed device in the upper diffusion chamber;
(c) connecting the upper diffusion chamber and the lower vacuum chamber so that a gas permeable membrane separates the upper diffusion chamber and lower vacuum chamber;
(d) subjecting the lower vacuum chamber to a vacuum whereby a pressure differential is effected across the membrane and gas in the first sealed device diffuses through the membrane;
(e) monitoring the gas diffused from the first sealed device and determining the time constant for the first sealed device to reach steady state diffusion;
(f) disconnecting the upper and lower diffusion chambers;
(g) removing the first sealed device and replacing with a second sealed device in the upper diffusion chamber;
(h) connecting the upper diffusion chamber and the lower vacuum chamber so that the gas permeable membrane separates the upper diffusion chamber and the lower vacuum chamber;
(i) subjecting the lower vacuum chamber to a vacuum whereby a pressure differential is effected across the membrane and gas in the second sealed device diffuses through the membrane;
(j) monitoring the gas diffusion from the second sealed device for a pre-determined portion of the time required in step (e); and
(k) determining the time required for the second sealed device to achieve steady state diffusion using the time constant.
17. The method of claim 16 further comprising:
configuring the air volume surrounding the first sealed device in the upper diffusion chamber to be below a preselected threshold.
18. The method of claim 17 further comprising:
configuring the air volume surrounding the second sealed device in the upper diffusion chamber to be below a preselected threshold.
19. The method of claim 16 further comprising:
positioning a slotted support member to support the membrane.
20. The method of claim 16 wherein the inert gas is helium.
21. The method of claim 16 wherein the first and second sealed devices are hard disc drives.
22. The method of claim 16 further comprising the step of monitoring the ambient pressure of air surrounding the first and second sealed devices in the upper diffusion chamber.
23. The method of claim 16 wherein the monitoring step for the first sealed device comprises:
maintaining the upper diffusion chamber substantially at atmospheric pressure on one side of the membrane as the opposing side of the membrane is subjected to the vacuum.
24. The method of claim 16 wherein the monitoring step for the second sealed device comprises:
maintaining the upper diffusion chamber substantially at atmospheric pressure on one side of the membrane as the opposing side of the membrane is subjected to the vacuum.
25. The method of claim 16 wherein each of the monitoring steps comprises:
measuring the diffused inert gas with a mass spectrometer.