While array CSPs have achieved most of the mind share-and market share-of the growing CSP market, leadframe CSPs are gaining in popularity. Leadframe CSPs offer a small footprint, a lower cost than most array-style CSPs (especially those built on a flex substrate) and a fixed body-size. Leadframe CSPs are often leadless, incorporating the leadframe within the package body so that only the bond pads show on the package underside. The major drawback to leadframe CSPs is that they cannot make use of the full I/O space available in an array I/O arrangement. Thus, leadframe CSPs are limited to low I/O-count devices. However, well over 50 percent of all ICs feature an I/O count of 32 or less, making the potential market huge. (The table presents a potentially conservative forecast for leadframe CSPs.) The original leadframe CSP on the market was the Lead-on-Chip (LOC), jointly developed by Hitachi Ltd., Hitachi Chemical Ltd. and Hitachi Cable Ltd. Hitachi Cable supplies the leadframes for this package. The package was designed a couple of years ago for the 64-megabit DRAM market, at a time when the devices were designed for center bond pads. The bond pads are now being transitioned to the perimeter of the chip.
Amkor Technology introduced its MicroLeadFrame (MLF) package in late 1999. The leads are flush with the package body, and the leadframe's metal die-attach paddle is exposed on the bottom of the package, enabling the use of down-bonds or conductive die-attach material, which in turn allows for a stable, low-impedance ground. Silicon Wave Inc. is using the MLF for its radio modem controller (RMC) products for Bluetooth wireless communications devices. ASAT Ltd. also offers a leadframe CSP, the Leadless Plastic Chip Carrier (LPCC). The die attach paddle feature provides premium thermal and electrical performance. A variety of ICs can be mounted into the package without altering the design of the etched copper leadframe. Fujitsu Microelectronics, Inc. offers the SON (small outline nonlead) package, and its BCC (bump chip carrier) package that has no leadframe. The BCC has a leadless, transfer-molded body with metal-plated terminals on the bottom. The terminals can be arranged so that the leads are on either two or four sides. Unlike the leadframe-based packages mentioned earlier, the BCC has terminal bumps that protrude beyond the package body forming a center air pocket beneath the die. Gold wire bonds connect to gold stud bumps within the terminals. The gold terminals bring the signal connection close to the ground plane, reducing leadframe inductance and capacitance. Fujitsu Microelectronics more recently introduced the BCC++ for RF devices in wireless applications. Conclusion The interest in leadframe CSPs has expanded significantly in the last year, probably because they are one solution to lowering the costs associated with CSPs. Given the tens of billions of low cost, low I/O-count ICs that are sold every year, leadframe CSPs can be expected to be a significant market.
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