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Many small holes need to be drilled in printed circuit boards to achieve a high packing density of circuit components. Even with NC control, conventional mechanical techniques are relatively slow and holes smaller than 035 mm diameter are difficult to achieve in production. Laser drilling has been suggested as a potentially fast technique capable of drilling small holes, so trials have been conducted on thin, flexible kapton board, and on 08 mm and 16 mm thick epoxide woven glass fabric board with 12 and 36 micron thick copper cladding. Using a 600 W CO2 laser, the proposed technique was to pre‐etch holes in the copper which would then act as a mask to the beam, so drilling only where etched holes existed. This technique was feasible on the flexible board, but not on the thicker boards because of damage to the copper. Using a pulsed Nd‐YAG laser to drill through both copper and laminate gave good results, but more work is necessary to eliminate occasional delamination of the copper around the hole. Through‐hole plating of the drilled holes appeared to present no special problems.

In the last two years, laser drilled microvias have become the dominant method for producing blind vias smaller than 150 mm, with over 100 laser drilling machines with a variety of laser types installed worldwide. Only a few of these systems have been qualified for drilling blind holes in standard glass reinforced FR4. Details a production line at Siemens AUT LP in Karlsruhe, Germany, involving the successful evaluation, introduction, and full production of laser drilling of FR4/glass. An ESI 5100 with Ultraviolet Nd:YAG laser operating at 355nm was chosen for all copper structuring and all microvias less than 150 mm in diameter in thin materials, and a TEA CO2 laser was chosen for thicker constructions, where at least 250 mm holes were required. Production has been running since November 1996. Details the process modifications, design rules, qualified materials, reliability tests, and production experiences.

As microelectronics continue to shrink, it is becoming increasingly difficult and expensive to mechanically drill very small via holes (<0·010 in.). Using lasers and optical technology, it is possible to drill any material. Thin circuit board materials of various compositions were investigated as candidates for laser drilling using a 100 watt CO2 laser. Laser variables were pulse frequency, duty cycle, and number of pulses (total energy delivered). Delivered energy seems to be the most critical parameter, and the optimal holes were drilled within a narrow energy band, although there was much data scatter. The best laser drilled holes were of lower quality than that obtainable with mechanical drilling. Photographs of the best holes in all materials are included.

There are many advantages of microvia: it requires a much smaller pad, which saves the board size and weight; with microvia, more chips can be placed in less space or a smaller PCB, which results in a low cost; and with microvia, electrical performance improves due to a shorter pathway. Basically, there are five major processes for microvia formation: NC drilling; laser via fabrication including CO₂ laser, YAG laser, and excimer; photo‐defined vias, wet or dry; etch via fabrications including chemical (wet) etching and plasma (dry) etching; and conductive ink formed vias, wet or dry. This paper will discuss the materials and processes of these five major microvia formation methods. At the end, eight key manufacturers from Japan will be briefly illustrated for their research status and current capability of producing smallest microvia.

Drilling blind vias with lasers has become more and more popular over the past three years as PWB fabricators and OEMs recognize the benefits of a process that has high throughput, is versatile with materials, has a fairly large process window and requires little to no changes in their existing manufacturing line. Laser drilling systems have improved in throughput over the past two years and as fabricators develop close working relationships with the laser system suppliers, better laser drilling systems emerge. This paper will discuss a laser drilling system that is a direct result of input from fabricators around the world. Details will be provided on compatible materials, and processing speeds.

The study aims to compare tribological properties between laser dimple textured surface and drilled dimple textured surface, and to analyze the influence of dimple hardened edges and ability of trapping wear debris on wear properties of dimple textured surfaces.

Circular textured dimples were produced on AISI 1,045 specimen surfaces using laser surface texturing (LST) and drilled surface texturing (DST) methods. Tribological behaviors of LST, DST and non-textured specimens were studied using ball-on-disc tribo-tester. Metallographic structures, dimples and worn surface morphologies were observed using a three-dimensional digital microscope. Hardnesses of substrate and dimple edges were measured.

There was no obvious difference in wear and friction coefficients between LST and DST specimens. Hardnesses of laser dimple edges were much higher than that of drilled dimple edges and specimen substrate. The hardened materials of laser dimple edge included recast zone and heat affect zone. Laser dimple was cone-shaped and drilled dimple was cylinder-shaped. Drilled dimple had a better ability of trapping wear debris than laser dimple. Non-uniform wear phenomenon occurred on worn surfaces of LST dimple specimens.

The ability of textured dimples to trap wear debris is affected by single dimple volume. Hardened edges of dimples cause non-uniform wear on worn surfaces of LST specimens.

Ball grid array (BGA) component packages challenge the circuit board design with signal routing and layout, creating in some cases extra board layers and added vias all resulting in increased costs for the printed circuit board (PCB). As component densities increase and microBGA (μBGA) and other fine pitch components become more common, microvia‐in‐pad technology will ease the transition to these fine pitch components. This paper presents and profiles a cost‐effective solution to interconnecting BGAs on PCBs using laser drilled blind vias connecting the outer three or more layers of a multilayer circuit board. Following a discussion on the design advantages, a comprehensive outline of the PCB fabrication process explores a new procedure for the rapid production of via‐in‐pad multi‐depth blind via laser drilling.

Recently, a Transverse Excited Atmospheric (TEA) CO2 laser technology has been developed for the micro‐machining of vias in non‐reinforced glass laminates. This system has been designed to accommodate the large panel sizes associated with PWB processing. The salient features of this modified CO2 laser technology are summarised. A joint Lumonics/Motorola study was carried out to assess the applicability of this laser processing technology for use in higher density PWB and MCM‐L substrate processing and its compatibility with currently available classes of dielectrics used in high density interconnect applications. A 10x improvement in cycle time/throughput over the existing raster scanning laser ablation process has been demonstrated.

The new Low Temperature Cofired Ceramic process combines the advantages of thick film standard and cofired ceramic technologies for the implementation of high interconnection density hybrid circuits, at a reasonable cost. Due to the wide diversity of devices required in the telecommunications field, it is important to have for drilling and scribing a system capable of being easily integrated onto a LAN, in order to reduce the machine preparation time, using all the information already existing in CAD. As laser systems are standard in thick film production, the investments involved to implement a new technology are minimised. This paper describes the use of laser technology for drilling green ceramic to achieve interconnection paths between different levels, manufacturing of screen mask (via metallisation), and scribing of substrates already synthesised. A preliminary characterisation of Telettra's technology follows.

Multichip module packaging enables a significant increase of interconnect densities and performance of electronic systems. Multichip module technology based on laminate materials (MCM‐L) is attractive due to low cost and use of the standard equipment used by PCB manufacturers. The most limiting factor for higher wiring densities in PCB technology is the mechanical drilling of plated‐through holes. Using 0.3 mm drill diameters, 0.5 mm land diameters are required, which limit the area for routing of tracks. Therefore, alternative dielectric materials, which can be structured photolithograpically, by plasma etching or laser drilling, are very attractive for MCM‐L technology. In this paper an epoxy resin layer, commercially available as a solder mask, is investigated as an interdielectric layer. Via hole drilling is investigated using an excimer laser. To show process feasibility, a two‐layer wiring system is fabricated using the excimer laser structured epoxy resin as an interdielectric layer on conventional epoxy board (FR‐4).