An improved apparatus has been designed and built for use in precise positioning and pressing of a microchip onto a substrate (which could, optionally, be another microchip) for the purpose of indium-bump bonding. The apparatus (see figure) includes the following:
- A stereomicroscope,
- A stage for precise positioning of the microchip in rotation angle (?) about the nominally vertical pressing axis and in translation along two nominally horizontal coordinate axes (x and y), and
- An actuator system that causes a bonding tip to press the microchip against the substrate with a precisely controlled force.
In operation, the microscope and the stage are used to position the microchip under the bonding tip and to align the indium bumps on the chip and the substrate, then the actuator system is used to apply a prescribed bonding force for a prescribed time.
The improved apparatus supplants a partly similar prior apparatus that operated with less precision and repeatability, producing inconsistent and unreliable bonds. Results of the use of the prior apparatus included broken microchips, uneven bonds, and bonds characterized, variously, by overcompression or undercompression. In that apparatus, the bonding force was generated and controlled by use of a micrometer head positioned over the center of a spring-loaded scale, and the force was applied to the microchip via the scale, which was equipped for digital readout of the force. The inconsistency of results was attributed to the following causes:
- It was not possible to control the bonding force with sufficient precision or repeatability. Particularly troublesome was the inability to control the force at levels less than the weight of 150 g.
- Excessive compliance in the spring-loaded scale, combined with deviations from parallelarity of the substrate and bonding tip surfaces, gave rise to nonuniformity in the pressure applied to the microchip, thereby generating excessive stresses and deformations in the microchip.
In the improved apparatus, the bonding tip and the components that hold the substrate and the microchip are more rigid and precise than in the prior apparatus, so as to ensure less deviation from parallelarity of the bonding-tip and substrate surfaces, thereby ensuring more nearly uniform distribution of bonding force over the area of the microchip. The bonding force is now applied through, and measured by, a load cell that makes it possible to exert finer control over the force. The force can be set at any value between 0 and the weight of 800 g in increments of 0.2 g.
This work was done by Larry Wild, Jerry Mulder, and Nicholas Alvarado of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Semiconductors & ICs category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive Pasadena, CA 91109-8099
(818) 354-2240
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Refer to NPO-35125, volume and number of this NASA Tech Briefs issue, and the page number.
This Brief includes a Technical Support Package (TSP).
Apparatus for Precise Indium-Bump Bonding of Microchips
(reference NPO-35125) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL), detailing an apparatus designed for precise indium-bump bonding of microchips. This technology is significant for aerospace applications, where the reliability and performance of microchips are critical. The document is part of NASA Tech Briefs, which disseminates information on technological advancements with broader scientific and commercial implications.
The bonding procedure outlined in the document emphasizes the sensitivity of the bonding tip, which must be handled with care to avoid damage. The process begins with the activation of the WildB bonder readout box, which requires a stabilization period of 10 minutes before use. Users are instructed to zero the readout box using the tare button and to ensure the optical flat is clean, utilizing isopropyl alcohol (IPA) for cleaning if necessary.
The bonding process involves several steps: aligning the chip under the bonding tip using a stereoscope, micro-aligning it with X, Y, and theta adjustments, and applying pressure gradually. Specifically, the bonding tip is lowered until a pressure of 15 grams is reached, applied at a rate of approximately 2 grams per second. After maintaining this pressure for one minute, the tip is raised at a rate of 5 grams per second. This cycle is repeated for each chip until all are bonded.
Figures included in the document illustrate various components of the bonding apparatus, such as the tip pressure micrometer and adjustment controls for precise alignment. The document also includes contact information for further assistance and emphasizes compliance with U.S. export regulations regarding the proprietary information contained within.
Overall, this Technical Support Package serves as a comprehensive guide for the bonding procedure, ensuring that users can effectively utilize the apparatus for high-precision microchip bonding, which is essential for the reliability of aerospace technologies. The document highlights NASA's commitment to sharing advancements in technology that may have wider applications beyond aerospace, fostering innovation and collaboration in various fields.
