It is often necessary to estimate the number of board layers in electronic modules before detailed routing is possible. Several methods for estimating board interconnect requirements prior to the existence of a netlist have been developed. Some estimation approaches depend on the use of heuristics derived from studying actually routed designs, while others depend on geometric or statistical arguments. The applicability and uncertainties associated with these estimation techniques are not widely understood. In this paper several different routing estimation methods are applied to a variety of printed wiring board and multichip module applications. The accuracy with which the methods predict the amount of required wiring is compared.
MCC has been developing the use of flashlamp pulsed Nd:YAG laser technology to bond TAB leadframes to bumped IC die. With basic equipment, the process has been proven in a laboratory scale environment. As a result, MCC recently licensed a vendor to manufacture the equipment so that it can be used in prototype and later in production environments. This project was initiated to develop a benign alternative for thermocompression gang bonding, particularly for applications where IC bond pads would be located over active circuitry. In addition, because the laser beam's positions are computer controlled, the process has shown to be very desirable for bonding conventional devices with peripheral pads, especially in high product mix applications. Bond rates of 40 bonds/second have been demonstrated at MCC. The first production prototype will bond at 60–80 bonds/s and it is anticipated that, with further development, the full production equipment will bond at 200 bonds/s. The process that is most mature at the time of writing is for bonding tin plated copper leads to gold bumps. This system allows formation of reliable bonds because the formed bonds consist primarily of copper and gold. The bonds are at least as strong and reliable as with other methods of TAB bonding. Bonds with this metallurgical system have been subjected to severe environmental testing without failure. This paper will present results of laser inner lead bonding, the equipment used to develop it and the expectations of the future equipment as well as the future of the technology itself.
A new method for bonding gold plated TAB leads to gold bumps is presented. This method uses a frequency doubled Nd:YAG laser which provides energy in both the visible (0.533 pm) and near IR (1.064 pm) spectra. This combination only 1.064 pm radiation where 98% of the radiation is reflected. which 2550% is absorbed by gold, is used to heat the gold used to form the bond. Bonding experiments were conducted and of wavelengths overcomes the difficulty of bonding gold with In the method presented in this paper, 0.533-pm radiation, of which becomes more absorptive to the 1.064-pm radiation that is samples were exposed to environmental testing. While there were 0 io00 ZOO0 3000-m e, f = AU initial bond failures, 85% of the bonds did not degrade during environmental exposure indicating the potential for the process. Temperatures ("C)~i~, 1, Melting and hiling points of materials of interest,
Since 1985, MCC has been developing the use of flashlamp pulsed Nd:YAG (YAG) laser technology to bond tape automated bonding (TAB) leads to I/O pads on integrated circuits (ICs). The I/O pads have 22 micron high gold bumps and the leads are copper plated, in the case described here, with electroless tin. As a result of the work presented here, a methodology has been developed that will result in a high throughput, reliable bonding process that overcomes the limitations of conventional thermocompression (T/C) and thermosonic (T/S) bonding technologies. In addition, because the position of the laser beam is software controlled, the process is very desirable for applications where a broad range of different IC form factors and sizes are to be bonded. Laser bonded devices have been exposed to degrading environments without failure, indicating the long term reliability of the process.
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