Thick-film hybrid circuits continue to dominate the hybrid circuit market because of their design flexibility, power handling capabilities and low production costs. In their simplest form, thick-film circuits consist of high purity alumina substrates with screen printed, fired resistors and conductors. The resistor materials are usually oxides of ruthemium with conductors of platinum/gold, palladium/gold, or palladium/silver.
Laser trimming of hybrid circuits, and more recently, monolithic IC's is often used to improve yields and/or device performance. As device technology advances, trim technology continues to evolve and now offers spot sizes under 4μm, positioning accuracy to lμm, positioning speed of a few ros, and field coverage of up to 8 inches; addressing such diverse applications as VLSI memory repair, and complete PC board assembly trimming. Increased automation in the form of fully automatic device loading, alignment and beam focus are resulting in vastly improved thruput and lowered manufacturing costs. New, faster, and more accurate instrumentation is being introduced to trim the new mixed digital/linear parts beyond the traditional restriction to simple passive resistance and functional DC trimming. Furthermore, trimmable device design has emerged from the "black art" catagory and predictable results can now be achieved. However, gaining familiarity with all aspects of functional trimming is a formidable task and this is a major reason more manufacturers haven't added laser trimming to their bag of tricks.
This paper describes a technique for generating photomasks for hybrid circuits using a laser resistor trimming system. Photomasks can be generated by two separate techniques: micromachining a thin opaque film on a transparent substrate with a Nd:YAG laser, or exposing a photoresist covered blank photomask with an argon ion laser.
The Nd laser has proved almost perfect for metal working and has been used to great advantage in the Philips Company. Experience over seven years shows increasing complexity in beam handling and the use of increasing higher powered lasers. Because of thermal lensing of the laser rod as a function of output power beam parameters as divergence angle and beam waist are seen to vary with output power. Above - 100 W one has to give due attention to this phenomenon and one has to use the proper laser resonator and focusing optics. In order to obtain the maximum benifit from laser welding one has to design products for this joining technique. Both weld geometry and the proper alloys should be chosen for reliable welding.
Pulsed CO2 TEA lasers are widely used in the electronics and semiconductor industries to mark passive components, hybrids and semiconductors. In addition to marking simple product identifying codes, an increasing requirement is to have the laser system mark variable information, derived from test results, on these products. This has required the development of laser beam delivery systems of increasing sophistication, capable of marking both alphanumerics and machine readable bar-codes, that are interfaced to test and process control equipment to permit high-speed, variable information coding.
Lasers continue to enter many exciting new fields that have been traditionally the domain of other equipment. Lately, lasers and their associated precision positioning equipment have replaced the more conventional methods used in the micromachining area because of better control, repeatability and precision. This paper discusses some of the latest applications of laser micromachining utilizing a medium-powered Nd:YAG laser. Topics will include machining ceramics, silicon and other materials as well as precise removal of thin films from various substrates. Some of the techniques created to accomplish the required results will be shown as well as improvements over previous methods.
The use of laser assisted-chemistry for dry etching of electronic materials is described. Emphasis is placed on the use of laser-assisted reactions for large area processing. Review of the current technology is given for large area masked etching, UV-projection etching, and laser assisted reactive ion etching (RIE), and plasma etching.
Modern Laser Wafer Trimming (LWT) technology achieves exceptional analog circuit performance and precision while maintain-ing the advantages of high production throughput and yield. Microprocessor-driven instrumentation has both emphasized the role of data conversion circuits and demanded sophisticated signal conditioning functions. Advanced analog semiconductor circuits with bandwidths over 1 GHz, and high precision, trimmable, thin-film resistors meet many of todays emerging circuit requirements. Critical to meeting these requirements are optimum choices of laser characteristics, proper materials, trimming process control, accurate modeling of trimmed resistor performance, and appropriate circuit design. Once limited exclusively to hand-crafted, custom integrated circuits, designs are now available in semi-custom circuit configurations. These are similar to those provided for digital designs and supported by computer-aided design (CAD) tools. Integrated with fully automated measurement and trimming systems, these quality circuits can now be produced in quantity to meet the requirements of communications, instrumentation, and signal processing markets.
This paper describes some of the potential applications of scanning laser generated images for use in material characterization, process control, and failure analysis in semi-conductor device manufacturing. Two applications are described in detail: CMOS latchup site identification and photoluminescence imaging of defects in gallium arsenide. Laser scanning is shown to be capable of identifying every site in a CMOS circuit which will sustain latchup under given bias conditions and identifying the relative sensitivities of each site. Photoluminescence imaging is shown to be capable of identifying the locations of dislocation clusters in gallium arsenide. These relatively inexpensive nondestructive tech-niques may prove to be powerful analytic tools in semiconductor device manufacturing.
A sensitive infrared detection system monitors the slight warming and cooling of a solder joint on a PWB in response to a focused laser beam pulse lasting for 30 milliseconds. Heating and cooling rates depend on the surface finish of the solder and also upon its interr.1 features. Joints which are alike show similar heating rates; defects behave differently and are flagged as showing abnormal thermal signatures Defects include surface voids, cold solder, insufficient or missing solder, residual solder flux, contamination and large subsurface voids. Solder bridges can usually be found by targeting at suspected bridge locations. Feed-through joints at DIPs and lap joints at flat-pack ICs are readily inspected by this method. By use of computer-controlled tiltable optics, access is had to the "harder to see" joints such as at leadless chip carriers and other surface mounts. Inspection rates can be up to 10 joints per second.