... for multilayer PCBs.3,4 Space-efficient routing between layers is necessary due to increased densities and reduced dependence on through-hole technology. Area-array packages such as BGAs, | PCB MAKER | CSPs, and flip chips shift the burden of interconnect fan-out to the PCB, increasing the need for higher wiring capacity. As the form factor for | PCB MAKER | such devices continues to shrink and I/O density mushrooms, the size and density of HDI microvias must follow suit. In 1997, for instance, the number | PCB MAKER | of microvias on a typical PCB panel was about 20,000. Now, a typical HDI panel contains about 250,000 microvias.4 | THE COMBINATION | of high | PCB MAKER | demand, abbreviated product cycles, shrinking IC packaging, and soaring interconnect densities places a high value on the development of cost-effective, high-volume microvia formation processes. | | PCB MAKER | HIGH-VOLUME MICROVIA | Formation Methods There are four techniques most commonly used to generate microvias: mechanical drilling, laser drilling, plasma, and photo (liquid or ...
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... set they can be dependably utilised for further processing and continued use. Due to the thin surface layer – a thickness of 0.15 – | PCB MAKER | 0.3 mµ is recommended – the surface of the pad is smoother and therefore there are, even in fine pitch areas, no restrictions when assembling. | PCB MAKER | The silver functions merely as a protection against oxidation, and the actual solder point is between the copper and chemical tin, therefore the solder point | PCB MAKER | is absolutely stable. It fulfills all UL requirements (UL796 specif.) and meets the usual requirements of automobile manufacturers: Test AlphaSTAR Result Requirement SIR 85°C/85%RH 2.46+9 | PCB MAKER | 24h Passed >1E+8;IPC-4553 IPC-TM-650 2.6.3.5. 3.15E+9 96h Passed SIR 35°C/85%RH 100VDC 3.56E+11 24h Passed >1E+10;IPC-4553 and GR-78 (Bellcore) IPC-TM-650 2.6.3.5 4.62E+11 96h Passed EM 10V | PCB MAKER | bias, 100V Test, 2.46E+9 24h initial Resistance no higher than the Power of 10 85°C/85%RH 1.18E+10 504 h (21 days) Passed Dendrites not Identified IPC-TM-650 | PCB MAKER | 2.6.14.1 Dendrites not ...
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... Nonetheless, the majority of laser-formed microvias are formed sequentially using the direct method rather than en masse using masks. CO2 lasers account for about | PCB MAKER | 80 percent of the lasers used for blind via and microvia formation. CO2 lasers can emit up to 225 watts of average power at a | PCB MAKER | wavelength of 9.4 microns, which is a good absorption wavelength for a large number of dielectric materials such as FR-4, RCF, polyimides, PTFE, and aramids. | PCB MAKER | This technology, however, requires capacity in wet chemistry and thermal oxidation for copper preparation. | THE PERFORMANCE CHARACTERISTICS | of RF-excited CO2 lasers enable them | PCB MAKER | to create microvias at high speed. In most dielectrics, for example, microvias can be formed sequentially at speeds of up to 450 microvias/sec. CO2 lasers | PCB MAKER | are used for resin-direct drilling (a common use in Japan) or for conformal mask drilling (common in Europe and the rest of Asia). The drilling | PCB MAKER | process is progressive and usually takes three pulses or shots to ...
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