Papers by Jim Hisert
by Jim Hisert , Jordan Ross , C.K. Merritt, Bob Jarrett
This paper relates the application of two of the methods
for testing the
thermal interface materials to the development and characterization of high performance materials. Particular strengths of different test methods provide a more complete understanding of TIM performance. In combination the tools provide effective development and improvement metrics. The limitations in resolution and repeatability are discussed.
TIM testing, ASTM D5470, thermal test vehicle
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Posted on 4 Mar 2010
by Thomas Acchione, Jim Hisert
Solar PV cell and module manufacturers are looking for new and improved assembly materials and process enhancements to increase throughput, reduce cost, and improve cell efficiency. To reach these (dynamic) higher goals for thin film deposition, new materials and cost-effective processes are needed. Depositing the target material directly onto the backing plate is typically used when conventional target bonding is simply not possible because of the low-melting point range of materials. When using the low melting alloys or single elements in thin film cells (CIG, CuGa, In, and InSn), it is possible to use a localized heat source to bond them at room temperature. This paper discusses:
1) the casting of these low-melting alloy sputtering targets, and
In addition, the presentation will demonstrate the bonding of low-melting point metallic sputtering targets, as well as how to verify the performance of these targets during operation.
solar, sputtering target, NanoFoil
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Posted on 21 Jan 2011
by Jim Hisert
Shrinking semiconductor package sizes, growing power handling and switching speeds are driving advances in electronic device cooling methods. Thermal conduction – the rate at which heat can be transferred away from these components – is key, but conventional
Thermal Interface Materials (TIMs) , at the limit of their capabilities, are becoming a bottleneck in the heat distribution pathway.
[Permanent Link to this Paper ]
Posted on 8 Mar 2010
by Paul Flynn, Jeff Schake, Jim Hisert
The wafer-level microsphere process is an accessible system of bumping a wafer with solder, which focuses on achieving high output at a low cost. This process begins with a wafer that has undergone front and back end-of-line procedures and is ready to accept solder as means of later interconnection. Flux is printed on the wafer UBMs (under bump metallizations) in a standard wafer paste type printing operation. This operation employs either a mesh screen or stencil to align flux deposits directly over the UBM. It is very common to use solder to act as an interconnect, while the UBM provides an attachment point for the solder, as well as a barrier to unwanted diffusion. The UBM also controls intermetallic formation. One common under bump metallization stack is titanium/nickel/gold. Each material has a purpose. In this example, titanium is used as an adhesion layer, nickel limits diffusion, and gold passivates the nickel to limit oxidation. After the flux is deposited, spheres of the correct size (typically 60 – 300um) are placed into the flux deposits and sent through reflow. The temperature for wafer reflow depends on the alloy, which is selected for the application. Tin/silver/copper alloys are very popular, although many people still use tin/lead and other low melting point alloys. The main consideration for choosing a certain alloy is often driven by processing restrictions during packaging or assembly. Sometimes a particular alloy is needed to endure life cycle testing or in-use conditions. Other lower temperature alloys are, at times, needed to allow the joining of die, which can not endure standard processing temperatures. The resulting solder formations should be spherical, with minimal height variations and maximum metallurgical attachment to the UBM. The flux can then be cleaned from the wafer surface if desired.
flux, spin coating
[Permanent Link to this Paper ]
Posted on 15 Oct 2009
by Jim Hisert , Brandon Judd
White Paper Video
Next Generation PoP Pastes for Electronics Assembly
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Package-on-package (PoP) technology allows two or more electronic components to be stacked vertically, which saves space and allows our portable gadgets to continue getting smaller year after year. A relatively new form of solder paste called "PoP Paste" has been developed specifically for this application.
There are fundamental differences between PoP pastes and the traditional solder pastes, which are designed for printing applications. This paper will highlight the differences between these solder pastes and talk about the characteristics needed by PoP pastes to increase transfer efficiency, eliminate head-in-pillow defects, and provide excellent solder wetting. If these three criteria are met, solder joint reliability will follow.
head-in-pillow, Dipping Flux, Dipping Paste, package on package, PoP Solder Paste, BGA
[Permanent Link to this Paper ]
Posted on 15 Oct 2009
by Jim Hisert
It is commonly known that Sn/Ag/Cu ball-grid array packages (BGA) are more brittle than Sn/Pb BGAs at
high stress levels such as those induced during drop testing. ¹ This problem is sometimes remedied by
reinforcing the solder joints with underfill. Even Sn/Pb area array packages are not always sufficiently
secure if attached without underfill.
Underfills have been designed to fortify both Sn/Pb and Pb-Free packages. Currently, the electronics
industry can choose from a few different underfill processes. Two of the most popular are the capillary
underfill (CUF) and no-flow underfill (NFUF) processes. In a drop-test, designed to mimic the realistic
abuse of portable electronics, packages assembled via each process were tested.
[Permanent Link to this Paper ]
Posted on 9 Mar 2010
by Jim Hisert , Sigurd R. Wathne PE
The best way to test a flux is to conduct the test in the production line under actual working conditions. This can be impractical if too many materials are included in the evaluation process. There are, however, ways to understand the capabilities of a wide range of flux materials without scrapping a large amount of production parts and time. This article will outline a test procedure that can be used to initially compare fluxes with minimal time, capital expense, and equipment. The key data is the quality of a flux to promote wetting of various alloys on a variety of surface finishes. [1] This will be calculated as a change in solder diameter after reflow. Although solder spread is the numerical outcome of the testing, cleanability of water-soluble fluxes and post reflow residue of no-clean fluxes may become apparent to the technician involved in this testing. It is a good way to get a feel for a material set in a very short time.
Solder Melting, Solder Basics, solder alloy, solder, pb-free, Flux Cleaning, flux, BGA, ball attach
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Posted on 1 Jan 2009
by Adrian Low, Jim Hisert , Andy C. Mackie PhD
Although there are some unsubstantiated claims that the history of solder reaches back 7000 years (Ref. 1), it seems more likely that the first
gold-tin solders were used in jewelry in the Egyptian Early Dynastic Era, around 5000 years ago (Ref. 2).
Why is solder still the overwhelming choice for interconnects when high-tech alternatives abound? The answer is simple: Solder is the only electrically conductive
joining material that is so compatible with the metal surface it is joining to that it intermingles on the atomic level.
Solder Melting, solder alloy, solder, pb-free, Flux Cleaning, flux, BGA, ball attach
[Permanent Link to this Paper ]
Posted on 15 Oct 2009
by Jim Hisert
The interconnection of solar cells is a technology that has been around for hundreds of years, but is a relatively new application of the soldering process. By combining the metallurgical knowledge of solder joints (which has been developed through other applications) and new materials designed specifically for solar manufacturing, solar cells and cell strings can be effectively connected with high throughput, conductivity, and reliability.
Stringing of solar cells is used across the solar industry, and is a process that newcomers to the solar industry should be familiar with. However, it is a process that even experts still need to optimize. The top layer of a solar cell is a transparent conductive oxide (TCO) to which solder will not adhere. Therefore, a metallization paste is used to bond to the TCO and provide a solderable surface for strips of solder-coated copper called tabbing or stringing ribbon. These ribbons are commonly applied as parallel strips that weave from the top of one cell to the bottom of the next to connect the positive and negative sides of the cells in series. Once connected, the tabbing ribbon channels electrical current to larger solder-coated copper strips, known as bus ribbon. Bus ribbon serves as an input/output for the entire solar array to the module junction box.
bus ribbon, flux, solar, tabbing ribbon
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Posted on 15 Oct 2009
by Jim Hisert , Andy C. Mackie PhD
Ball-attach fluxes for
solder sphere attachment processes are just one example of how fluxes used within the semiconductor market have evolved significantly. Process needs for water-soluble fluxes have sparked the necessary advancements for developing products that meet these
requirements.
[Permanent Link to this Paper ]
Posted on 10 Mar 2010
