Printed Circuit Design & Fab - February 2008 - (Page 42)

TABLE 3. Quality and reliability with NovaspeedTM. CHARACTERISTICS ■ Flat, Smooth, Thin Glass Weave ■ DirectFinish Technology ■ Homogeneous Spread Fiber Weave ■ No Hollow Fibers QUALITY/RELIABILITY IMPROVEMENTS ■ Laser Drilling – time/cost savings, hole quality ■ Mechanical Drilling ■ CAF Resistance ■ Higher Production Yield TABLE 4. Performance improvements with NovaspeedTM. CHARACTERISTICS ■ Flat, Smooth, Thin Glass Weave ■ Low Dk/Df ■ Homogeneous Spread Fiber Configuration PERFORMANCE IMPROVEMENTS ■ Homogeneous Dk/Df ■ Less Impedance Variation ■ Reduced Signal Skew, Improved SI However, addressing the issue by glass style alone does not improve upon the other important aspects discussed above. Indeed, laminate core thickness below about 4 mils cannot be achieved using these heavier fabric styles. Conclusion Based on the known characteristics of this advanced glass fabric, direct improvements can be predicted. The flat, smooth laserdrillable glass fabric will have improved laminate surface planarity and inherently lower surface roughness, as compared to laminate made with traditional glass fabrics. Improvements in “telegraphing,” laser-drilled hole geometry, hole plating quality and laser drilling speed can be expected. Where mechanical drills are used, a reduction in drill wander can also be expected. Furthermore, the high strength properties of a directly finished fabric, combined with the more uniform distribution of the glass fiber yarns, provides improved dimensional stability in circuit board laminate applications. The use of a direct finishing technology combined with the spread fibers of untwisted yarn results in greatly improved wettability and resin impregnation (of the glass bundles), and therefore the highest quality glass-to-resin bond is ensured. This property is the main factor in improved CAF resistance. An electrochemical migration phenomenon similar to CAF is caused by hollow fibers. This low Dk glass fabric exhibits zero hollow fibers. TABLE 3 summarizes these characteristics with corresponding quality and reliability improvements. TABLE 4 identifies performance improvements that result in the fabric with the combination of an improved finishing method, a non-twist glass, and a proprietary low Dk glass formulation. The printed circuit substrate exhibits a homogeneous Dk and Df, leading directly to less impedance variation and reduced signal skew, resulting in improved signal integrity. An advanced glass fabric has been utilized in several high performance com- mercial resin systems to generate test panels with superior electrical properties at 10 GHz. However, by using a unique manufacturing process and proprietary low Dk glass formulation, a homogeneous reinforcement layer has been developed that is unlike traditional glass fabrics. In fact, the key features of this proprietary technology are not addressed by existing industry specifications. It is expected that FWE can be completely eliminated as a performance constraint in high speed PCB susbstrates with the use of this novel technology. This new glass fabric could represent a paradigm shift for PCB substrate performance. PCD&F RUSSELL S. DUDEK JR. is a technology specialist at Compunetics; rdudek@ compunetics.com. JOHN J. KUHN is VP and CTO and PATRICIA GOLDMAN is manager, technical services, at Dielectric Solutions; jkuhn@dielectricsolutions. com, pgoldman@dielectricsolutions.com. Test Results TABLE 1 shows initial test data on glass fabrics. The thickness measurements are per ASTM D579 (25 psi). Dielectric constant (Dk) and dissipation factor (Df) for the NovaSpeed 1080 fabric was measured at 10 GHz using the NIST split cavity method at the Materials Research Lab at Pennsylvania State University10. These measurements were subsequently corroborated by calculations from test laminates per IPC-TM-2.5.5.5 (stripline method). The traditional 1080 Dk and Df measurements were taken from a table compiled by the IPC 3-12d Glass Reinforcement Task Group and represent data from four global manufacturers of E-glass yarn11. As previously described, the Dk of the NovaSpeed glass fabric is lower than that of E-glass in traditional fabric. More precisely, the Dk of this fabric is midway between that of E-glass and typical high performance resin systems. Thus the Dk difference between glass and resin is half of that seen in typical laminate products. TABLE 2 shows Dk and Df results at 10 GHz with the low Dk 1080 glass fabric alone, and with three commercially available resin systems. These resin systems, while high performance, are not characterized as “exotic” but are considered to be “FR-4 processable.” The bulk glass measurements were done using the NIST split cavity method and all other measurements are per IPC-TM650 2.5.5.5 stripline method. 42 REFERENCES 1. K. Dietz, “Fine Lines in HighYield (Part XCVIII): Advances in Reinforcement Structures, Tech” Talk in CircuiTree, November 2003. 2. G. Brist, B. Horine, G. Long; “High Speed Interconnects: The Impact of Spatial Electrical Properties of PCB due to Woven Glass Reinforcement Patterns, S18-5-1, IPC Expo/ ” SMEMA Council/APEX/Designers Summit 2004. 3. E. Bogatin, S. Zimmer, “Achieving Impedance Control Targets, Printed Circuit Design ” & Manufacture, April 2004. 4. S. McMorrow, C. Heard, “The Impact of PCB Laminate Weave on the Electrical Performance of Differential Signaling at MultiGigabit Data Rates, DesignCon East 2005. ” 5. E. Bogatin, “Skewering Skew, Printed Cir” cuit Design & Manufacture, April 2005. 6. J. Loyer, R. Kunze, X. Ye, “Fiber Weave Effect: Practical Impact Analysis and Mitigation Strategies, CircuiTree, March 2007. ” 7. L. Ritchey, “Intelligent Design, CircuiTree, ” April 2007. 8. J. Kuhn, “Advanced Reinforcement Technology Presents New Design Opportunities for Printed Circuit Boards” ECWC 10 Confer, ence at IPC Printed Circuits Expo/APEX/ Designers Summit 2005. 9. IPC-4412A, “Specification for Finished Fabric Woven from “E” Glass for Printed Boards, ” January 2006, IPC, Bannockburn IL.. 10. NIST Split Cavity method for measurement of relative permittivity [Dk] and loss tangent [Df], subsequently standardized as IPC-TM-650 2.5.5.13. 11. Committee Report of Woven Glass Reinforcement Task Group 3-12d from IPC Apex/Expo 2007 (ipc.org/CommitteeDetail. aspx?Committee=3-12D). FEBRUARY 2008 PRINTED CIRCUIT DESIGN & FAB http://ipc.org/CommitteeDetail.aspx?Committee=3-12D http://www.ipc.org/CommitteeDetail.aspx?Committee=3-12D

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - February 2008

Printed Circuit Design & Fab - February 2008 Contents Our Line Market Watch Around the World Happenings ROI Tip Jar Interconnect Strategies IC/PCB Co-Design Modeling Design Tools Optical Interconnect Trade Shows Laminate Materials Off the Shelf Marketplace Ad Index BGA Bulletin

Printed Circuit Design & Fab - February 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.