Leak Testing Methods and Systems

• US 20130325371A1
• Filed: 06/05/2013
• Published: 12/05/2013
• Est. Priority Date: 06/05/2012
• Status: Active Grant

• Current Assignee: Sciemetric Instruments Inc. (TASI Holdings, Inc.)
• Original Assignee: Sciemetric Instruments Inc. (TASI Holdings, Inc.)
• Inventors: Brine, Richard Michel, Sheaff, Nathan Bernard
• Granted Patent: US 9,377,374 B2
• Time in Patent Office: Days
• US Class Current: 702/51
• CPC Class Codes: G01M 3/26 by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
• CPC Class Codes: G05D 7/0629 characterised by the type of regulator means

Abstract

Leak rate testing is an engineering challenge where on the one hand, engineers must meet strict leak rate standards on a wide range of products and systems from semiconductor packages through medical product packaging to chemical storage vessels and liquid/gas handling systems. On the other hand, they have to make the leak testing process low cost and independent of operator whilst in many applications making the process automated and fast as this step may otherwise become a manufacturing bottleneck. Accordingly embodiments of the invention address manufacturing requirements by providing for high accuracy flow based leak testing of large volumes, providing adaptive techniques for use during testing, providing equivalent circuit modeling techniques allowing optimization and parameter extraction to be simulated prior to manufacturing commitment, and providing for the automatic tuning of setup parameters.

Claims

1. A method of leak testing a device under test (DUT) comprising the steps of:

a) filling the DUT with a fluid to a predetermined pressure using a first regulator R2 and first valve V1 disposed in series between a source of the fluid and the DUT via a first process sequence comprising a first set of characteristics;

b) measuring with a high accuracy flow controller F1 a measured flow waveform via a second process sequence comprising a second set of characteristics; and

c) calculating with a microprocessor a leak rate for the DUT in dependence upon at least the measured flow waveform.

2. The method of leak testing a DUT according to claim 1 wherein,

at least one of the first set of characteristics and the second set of characteristics were established using a process comprising the steps of:

automatically operating a leak test system comprising at least the absolute test pressure sensor P1 measuring the fluid pressure in proximity to the DUT, the high accuracy flow controller F1 for controlling fluid provided to the DUT, and a controller processing the output of the absolute pressure sensor to generate a setting for the high accuracy flow controller F1;

automatically executing a predetermined subset of test sequences of a plurality of test sequences with the leak test system;

storing in a memory associated with a computer a plurality of measurements taken during each test sequence of the predetermined subset of test sequences of a plurality of test sequences;

automatically determining in dependence upon a predetermined portion of the plurality of measurements at least one characteristic of a plurality of characteristics, each characteristic relating to at least one of the leak test system, the DUT, and an overall test time for performing a leak test to a predetermined specification.

3. The method of leak testing a DUT according to claim 1 wherein,

at least one of the first set of characteristics and the second set of characteristics were established using a process comprising the steps of:

automatically operating a leak test system comprising at least the absolute test pressure sensor P1 measuring the fluid pressure in proximity to the DUT, the high accuracy flow controller F1 for controlling fluid provided to the DUT, and a controller processing the output of the absolute pressure sensor to generate a setting for the high accuracy flow controller F1;

automatically executing a predetermined subset of test sequences of a plurality of test sequences with the leak test system;

storing in a memory associated with a computer a plurality of measurements taken during each test sequence of the predetermined subset of test sequences of a plurality of test sequences;

automatically establishing an equivalent electrical circuit model of the leak test system and DUT in dependence upon at least the plurality of measurements;

automatically determining in dependence upon a predetermined portion of the plurality of measurements at least one characteristic of a plurality of characteristics, each characteristic relating to performing a leak test to a predetermined specification and established in dependence upon the equivalent electrical circuit model.

4. The method of leak testing a DUT according to claim 1 wherein,

step (b) further comprises correcting the measured flow waveform for adiabatic processes impacting the DUT during a test sequence of which step (b) forms part, the correction being determined by establishing a nominal curve for the DUT through the steps of:

(i) executing a plurality of leak test sequences of a single design on a plurality of DUTs and storing at least one of the entire pressure curve and the entire flow curve as their measured flow waveform;

(ii) temporally aligning the plurality of measured flow waveforms using at least one significant attribute of the plurality of measured flow waveforms; and

(iii) statistically processing the plurality of aligned measured flow waveforms to establish the nominal curve.

5. The method of leak testing a DUT according to claim 4 wherein, correcting the measured flow waveform for adiabatic processes impacting the DUT comprises:

(iv) performing an alignment process on the new test data for the DUT under test;

(v) subtracting the nominal curve from the new test data; and

(vi) using the adjusted test data to determine the leak rate.

6. The method of leak testing a DUT according to claim 1 further comprising;

filling a tank with the fluid to the same predetermined pressure as the DUT, wherein

the tank and DUT are fluidically linked and the high accuracy flow controller F1 is disposed within the fluidic link between the tank and DUT.

7. The method of leak testing a DUT according to claim 6 further comprising;

automatically performing an automatic parametric process as part of the leak testing process to determine the specific volume of each DUT tested.

8. A method of leak testing a device under test (DUT) comprising the steps of:

a) establishing a leak test protocol comprising at least a first set of characteristics related to at least one of a filling and stabilization process, a second set of characteristics related to a testing process, and a third set of chracteristics relating to an exhaust process;

b) preparing the DUT with a fluid to a predetermined pressure using a first regulator R2 and first valve V1 disposed in series between a source of the fluid and the DUT via a first process sequence comprising the first set of characteristics;

c) measuring with a high accuracy flow controller F1 a measured flow waveform via a second process sequence comprising the second set of characteristics;

d) performing an exhaust process to allow replacement of the DUT; and

e) calculating with a microprocessor a leak rate for the DUT in dependence upon at least the measured flow waveform.

9. The method of leak testing a DUT according to claim 8 wherein,

establishing at least one of the first set of characteristics, the second set of characteristics, and the third characteristics comprises:

performing a leak test protocol to establish a plurality of data sets at each setting of an aspect of a leak test protocol as it is varied between a lower limit and an upper limit;

performing statistical analysis of each data set to establish at least a standard deviation of that data set; and

selecting the setting of the aspect of the leak test protocol having the lowest standard deviation.

10. The method of leak testing a DUT according to claim 8 wherein,

steps (b) and (c) are performed concurrently;

and

step (c) further comprises applying a mathematical model to the measured flow waveform in order to at least one of predict the DUT leak rate and terminate the leak rate measurement if the measured flow waveform exceeds by a predetermined amount the modeled flow waveform for a DUT at the limit of acceptable leak rate.

11. A method of leak testing a device under test (DUT) comprising:

providing a leak testing pneumatic circuit comprising at least an inlet for connection to a source of fluid, a pressure regulator, a first valve coupled to the regulator and a second valve, a pressure sensor coupled to the output of the second valve, and an outlet coupled to the output of the second valve for coupling to the DUT;

executing a leak test sequence for a DUT by cycling the first and second valves through a predetermined sequence to selectively perform at least one of a system check, a filling step, a stabilization step, a testing step, and an exhaust step;

wherein

the output of the pressure sensor is continuously acquired by a microprocessor to perform a full flow waveform analysis as part of a quality assurance step for the DUT.

12. The method of leak testing a DUT according to claim 11 wherein,

the leak test sequence is established according to a process comprising the steps of:

executing a predetermined test sequence of a plurality of test sequences with the leak testing pneumatic circuit;

storing in a memory associated with a computer a plurality of measurements taken during a predetermined portion of the predetermined test sequence;

determining in dependence upon a predetermined portion of the plurality of measurements at least one characteristic of a plurality of characteristics, each characteristic relating to the leak testing pneumatic circuit and the DUT.

13. The method of leak testing a DUT according to claim 11 wherein,

during a system check step of the leak test sequence statistical analysis of the pressure sensor output waveform is performed to assess whether at least one of the average and peak-to-peak variation of the output waveform exceed predetermined thresholds which are indicative of a fault condition of the leak test pneumatic system.

14. The method of leak testing a DUT according to claim 11 wherein,

during the leak test sequence transient analysis of the pressure sensor output waveform is performed to assess at least one of whether an element forming part of the DUT moved during the test and the movement exceeded an acceptable limit.

15. The method of leak testing a DUT according to claim 11 wherein,

during at least one of the filling step and the exhaust step of the leak test sequence analysis of the pressure sensor output waveform is performed to detect an anomaly within at least one of the leak test pneumatic system and the DUT.