Chips assembly

The Protein Profiling Biochip is composed of six chips assembled in a flow cell cassette device. Each chip provides 200 data points (200 pillars per chip) for a total of 1200 data points per cassette. Pillars are 50 p in diameter. The mesa on each pillar is covered with a self-assembled monolayer (20 to 25 A thickness) of biotin-derivatized PLL-g-PEG groups. A constant grafting ratio of 3.5 parts Lys to 1 part PEG is maintained with variable biotin-PEG content. sAV antibody is immobilized at 0.5 to 2 pmole/cm and Fab fragments at 4 pmole/cm. ... 

The structure is bonded to a substrate 24 which is chosen to have a coefficient of thermal expansion that is selected for providing the resultant read-out chip assembly with an effective coefficient of thermal expansion that is approximately the same as an HgCdTe detector array 36. The substrate material may be GaAs (4.5-5.9 x 10"6 m/mK), CdTe, Ge (5.5-6.4 x 10"6 m/mK), and a-plane sapphire (3.5-7 5 x 10" m/mK) where the coefficients of thermal expansion are given in parentheses. The coefficients of thermal expansion for silicon, HgCdTe and epoxy are 1.2 x 10"6 m/mK, 3.8-4.5 x 1 O 6m/mK and 30-50 x 10"6 m/mK, respectively. Next, the substrate 16 is removed and aluminium pads 34a are formed. Indium bumps 34b are cold welded to corresponding indium bumps 36b. 

FIGURE 1.12 Chip assembled on standard TO-8 package. (Reprinted from Sens. Actuators B, 58, Horrillo M.C., Sayago L, Ares L., Rodrigo J., Gntierrez J., Gotz A., Gracia I., Fonseca L., Cane C., and Lora-Tamayo E., Detection of low NO2 concentrations with low power micromachined tin oxide gas sensors, 325-329, 1999, with permission from Elsevier.)... 

DeBarros T, Katze D. Achieving SMT compatible flip-chip assembly with no-flow underfills. Proc. NEPCON West Conf Anaheim, CA 2000. 

Conductive adhesives are one of the feasible alternatives to lead for electronics assembly. Isotropically conductive adhesives are suitable for standard pitch (50- to 100-mil) surface-mounted components and numerous commercial materials are available (see commercial suppher Ksting, Section VI.E). Anisotropically conductive adhesives are more suited to flex to rigid connections, fine pitch components (15- to 20-mil pitch), and flip-chip assembly (4- to 12-mil pitch) [22]. Adhesives are not ready to replace solder throughout the electronics industry, however, due to questions that remain concerning the reliability of electrical interconnections. Their implementation is currently limited to low-cost applications using polyester substrates and specialty appHcations where solder cannot be used. Additionally, the lack of equipment for large-volume assembly with anisotropically conductive adhesives, which require the simultaneous appUcation of heat and pressure, impedes the acceptance of these promising materials. 

Data describing the reliability of joints assembled with anisotropically conductive adhesives are incomplete. Several papers have been published, but usually the sample size investigated is small, the accelerated stress tests are not standardized, and the results are highly dependent on device type (e.g., flexible circuit to rigid PWB, surface-mounted components, and flip-chip assembles). Further work is required in this area. 

DeBarros, T., and Katze, D., Achieving SMT Compatible Flip-Chip Assembly with No-Flow Underfills, Proc. NEPCON West Conf., Anaheim, CA (2000)... 

Anodic Bonding, Fig. 3 Microreactor chip assembly by anodic bonding of silicon and glass... 

Electrophysiology Recordings To record currents from sealed cells, the silicon chip assembly was used as a chamber for a voltage clamp setup (Fig. 6). Each half of the chamber (top and bottom) was connected to the electrodes of a headstage. The top chamber was connected to the input of the patch clamp amplifier, and the bottom chamber was connected to either the ground or the command voltage depending on the amplifier used. 

By an FEM analysis for the second-level interconnection, we found that the stress yielded by the TCE mismatch between the substrate and the PWB reaches a minimum value when the TCE is around 11 ppm/°C for a flip chip assembly type packages [5]. We developed a high TCE ceramic material, in which the TCE and the Young s modulus are 11.5ppm/°C and 114GPa, respectively. 

New High TCE Ceramic Material for Wire Bonded Chip Assembly Type CSP with Potting Compound... 

Evaluation of Temperature Cycling Test for wire bonded chip assembly type CSP... 

FIGURE 1.1.9 Photograph of cross-sectional SEM of solder joints of TCT (—40 to 123°C) samples of wire bonded chip assembly type CSP made of the 11.3 ppm/° C material after 1000 cycles. 

FIGURE 1.1.13 Solder joint reliability by TCT (—40 to 125°C) for flip chip assembly type CSP made of the high TCE ceramic material. 

ACA flip chip technology has been employed in many applications where flip chips are bonded to rigid chip carriers (13). This includes bare chip assembly of ASICs in transistor radios, personal digital assistants (PDAs), sensor chip in digital cameras, and memory chip in lap-top computers. In all the applications, the common feature is that ACA flip chip technology is used to assemble bare chips where the pitch is extremely fine, normally less than 120 /rm. For these fine applications, it is apparently the use of ACA flip chip instead of soldering which is more cost effective. 

Fig. 7. Schematic depicting a flip chip assembly processing utilizing ABC adhesive, (a) A chip is aligned to the ABC preform which is on a carrier film, (b) The ABC preform is tacked to the die at 100°C and imder a pressure of 150 g for 30 s, and then the carrier film is removed after the chip is cooled down, (c) The chip with ABC preform is aligned to a mating chip carrier (FR4 board), (d) The chip/ABC preform is attached to the chip carrier at 100°C and under a pressure of 150 g for 30 s, and then the package is cooled down.

Underfill. An underfill is then injected into the gap between the chip and chip carrier and then cured to complete the flip chip process. The function of the underfill or encapsulation as it is sometimes referred to is to provide mechanical integrity and environmental protection to a flip chip assembly. Studies have demonstrated that both thermoset and thermoplastic ICAs can offer low initial joint resistances of less than 5 mS2 and stable joint resistances (Au-to-Au flip chip bonding) during all the accelerated reliability testing listed in Table 1. The reliability results have indicated that there is no substantial difference in the performance of thermoset and thermoplastic bumps and both types of polymers apparently offer reliable flip chip electrical interconnections (53). 

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