Bumped chip carrier

BCC Bumped Chip Carrier, PDA Personal Data Assistant. Technology licensed to Amkor NA - Not Available. 

Standard bumped chip carrier (BCC) and electrically/thermally enhanced (BCC+) center-exposed-pad technology, overmolded Structure without interposer for low standoff height BCC (Fujitsu) Flash memory, portable electronics... 

Standard bumped chip 40% less mounting area an carrier and electrically/ 67% less mounting volume... 

Fig. 4. Schematic illustration of the formation of electrical interconnects between a bumped chip and a mating carrier using a Bi-filled ACA. (a) The chip is aligned and placed on a chip carrier, (b) The Bi particle is deformed between a chip bump and a carrier pad when a bonding pressure is applied, (c) The Bi particle dissolves into the liquid lentils upon exposure of heat, (d) Bi diffuses into the Sn-Pb matrix and forms fine solid precipitates.

ACA Bumped Flip Chips for High Frequency Applications. The high frequency behavior of ACA interconnections has attracted much attention in the past several years. Sihlbom and co-workers demonstrated that ACA-bonded flip chips can provide performance equivalent to solder flip chips in the frequency range of 45 MHz to 2 GHz on FR4 chip carriers and 1 to 21 GHz on a high frequency Telfon-based chip carrier (Fig. 5). The different particle sizes and materials in the conductive adhesives gave little difference in high frequency behavior of ACA joints (22,23). 

Fig. 6. Illustration of a scheme for fine pitch, flip chip interconnection, (a) An ACF filled with micrometallic columns, (b) A typical cross-sectional structure of a chip without bumps and the mating chip carrier, (c) A cross section of an interconnect formed between an unbumped chip and the mating chip carrier.

ChipPAC, Inc., demonstrated an alternate process/package concept covering both CSP and PBGA package formats whose construction is illustrated in Figure 8. The concept package consisted essentially of three parts ACF, metallic bumps on the die bond pads, and an organic chip carrier (29). 

The combination of cured adhesive interconnection, bumps, and organic substrate provides a reliable, cost-effective flip chip CSP. It was determined that Au-stud bumps were preferable to Ni/Au bumps because of the former s compliant nature. Since the planarity control of organic chip carriers is difficult, given the nature of the material, it was simpler to change the interconnection method, ie, using Au-stud bumps. However, electroless Ni/Au bumps are still an option, if the material properties of the ACF and/or chip carrier are altered to provide compliancy. 

Once the bumped wafers are diced, chips are picked from the wafers, flipped over, and then placed on and bonded to chip carriers. Different process procedures are utilized to bond thermosetting polymer bumps to similar thermoplastic bumps, as noted in Figure 13. Final processing involves a heat cure for thermosetting bumps, while thermoplastic bump connections only require in a few seconds under heat and pressure to melt the thermoplastic. 

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). 

Chips with thermoplastic bumps are placed on chip carriers and preheated to approximately 20°C above the melting point of the polymer, causing the bumps to melt onto the matching chip carrier pads. Mechanical and electrical bonds are... 

Fig. 14. Schematic depicting a flip chip technology utilizing chips with micromachined poljrmer bumps, (a) Process flow for creating micromachined polymer bumps in the wafer state, (b) Die attachment to a chip carrier.

Another process for bonding a flip chip with metal bumps consists of screen printing an ICA on a chip carrier, aligning and placing the chip, curing the ICA to form bonds, and imderfilling. By using this approach, SINTEF Electronics conducted a comparison study between an ICA-bonded and solder-bonded flip chips on FR4 chip carrier with Ni/Au metallization. The number of thermal cycles (—55 to 125°C) to failure for both solder and ICA flip chip circuits was compared. The study showed that stable contacts could be maintained for at least 1000-2000... 

Die (semiconductor) The conductor circuit pattern on the surface of a chip that is connected to a printed circuit board or chip carrier by wires (to a lead-frame) or solder bumps (Flip-chip bonding). 

Flip-chip bonding (semiconductor processing) When the circuit die is connected directly to the printed circuit board or chip carrier by means of solder bumps. See also Die. 

A second flip chip technique is realized by the use of eutectic Pb-Sn or other low-melting-temperature solder bumps in place of high-Pb solder bumps. These chips can be directly reflow attached to the chip carrier using low temperature. In this application, the chip carrier can be either ceramic or an organic laminate. 

In one study [29] the formation of intermediate alloys in Sn-3.4Ag-0.7Cu/metal systems was investigated for Ni and Cu metallization (with the same die and Ni-V die metallization). In producing these samples, a Cu-Ag-Sn solder paste was printed onto Ni-V die terminal pads and reflowed. The resulting solder bumps were fluxed and reflowed a second time in order to attach them to an OSP-coated Cu metallization or Ni/Au/Cu metallization on a chip carrier. The chips were reflowed under standard industrial conditions. A second reflow was conducted to attach the solder to either a Ni or a Cu metallization. This reflow consisted of peak temperatures between 234° and 250°C, and times above the liquidus temperature ranging between 50 and 80 sec. 

B. ACA-Bumped Flip Chips on Glass Chip Carriers... 

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