US3889122A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of determining bond quality of power transistors attached to substrates
Assignee: National Aeronautics and Space Administration
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Filing: 1974-04-26
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Granted: 1975-06-10
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Expires: 1994-04-26
Abstract
Abstract A method of determining the quality of the bond between a power transistor and an electrically insulative, heat conductive substrate includes taking X-ray exposures of the bond. In the exposures, the areas where the bond quality is poor show up as dark spots in relation to a lighter background area where the bond quality is good. The exposures are tested in a light meter device in which the average transparency of an exposure indicates the percentage of voids, or poorly bonded areas. Only those units having less than a predetermined percentage of voids are acceptable.
Inventors
- 👤 James C Administrator Fletcher
- 👤 Thomas A Telfer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 18:37
CPC Classifications
G; G01; G01N; G01N23/00; G01N23/02; G01N23/04; G01R; G01R31/00; G01R31/28; G01R31/302
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
130 words
A method of determining the quality of the bond between a power transistor chip and a heat conductive, electrically insulating substrate between which is a thin layer of bonding material, the chip, substrate and material in combination constituting a unit, comprising: a. selecting an index of bond quality for a production run unit in terms of the ratio that the area of bond voids in a minimally acceptable unit bears to the entire bond area; b. X-raying the bond area of a production run unit to obtain an X-ray exposure transparency; c. measuring the average optical density of the transparency; and d. comparing the measured average optical density of the transparency with the index to determine the bond quality of the production run unit relative to a minimally acceptable unit.
Claim 2
Independent Claim
130 words
A method of determining the quality of the bond between a power transistor chip and a heat conductive, electrically insulating substrate between which is a thin layer of bonding material, the chip, substrate and material in combination constituting a unit, comprising: a. selecting an index of bond quality for a production run unit in terms of the ratio that the area of bond voids in a minimally acceptable unit bears to the entire bond area; b. X-raying the bond area of a production run unit to obtain an X-ray exposure transparency; c. measuring the average optical density of the transparency; and d. comparing the measured average optical density of the transparency with the index to determine the bond quality of the production run unit relative to a minimally acceptable unit.
Claim 3
Dependent Claim
82 words
A method according to claim 1 wherein the index is selected by: a. obtaining X-ray exposure transparencies of the bond areas of a number of test units; b. measuring the average optical density of each transparency; c. examining the bond of each test unit to determine its quality; and d. correlating the bond quality of each test unit with the average optical density of the transparency associated with the test unit to obtain the index of bond quality foR production run units.
Claim 4
Dependent Claim
25 words
A method according to claim 2 wherein the X-ray transparencies are taken with the X-rays impinging on the outer surface of the chip perpendicular thereto.
Claim 5
Dependent Claim
38 words
A method according to claim 3 wherein the average optical density of a transparency is measured by placing the transparency between a light source and a light meter whose deflection is a measure of the average optical density.
Claim 6
Dependent Claim
18 words
A method according to claim 4 wherein all of the X-ray transparencies are taken under the same conditions.
Claim 7
Dependent Claim
33 words
A method according to claim 5 wherein the index is 20 percent so that a production run unit whose ratio of bond voids to the entire bond area exceeds the index is rejected.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-06-09 | 1978-12-09 | 1979-06-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-06-09 | 1982-12-09 | 1983-06-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-06-09 | 1986-12-09 | 1987-06-10 | $7700.00 | Window Closed / Lapsed |