Printed Circuit Design & Fab - January 2009 - (Page 20)

LAMINATE MatErialS Making SenSe of Laminate Dielectric Properties Understanding material properties reduces the design cycle, facilitates stack up and provides a cost to performance advantage. by RICHARD PANGIER and MICHAEL J. GAy System operating speeds continue to increase to answer consumer demand for such technologies as faster Internet connectivity, video on demand and mobile communications. As a result, high performance printed circuit board (PCB) substrates have emerged to address signal integrity issues at higher operating frequencies, commonly called low Dk and/or low loss Df materials. The published “typical” values found on a product data sheet provide limited information, usually a single construction and resin content, and are derived from a wide range of test methods and test sample configurations. A PCB designer or front end application engineer must be aware that making a design decision based on the limited information found on a product data sheet can lead to errors which can delay a product launch or increase the assembled PCB cost. To help designers, the following presents critical selection factors that go beyond a typical product data sheet and explains how these factors must be considered when selecting materials for high-speed applications. Whether making a decision to buy electronic equipment, a mobile phone or substrate material, one of the first places a person looks is to the technical data sheet. The data sheet provides a snap shot of the product attributes that can be used 20 to compare similar taBlE 1. Mid Dk resin system properties. thickneSS (milS) cOnStructiOn reSin cOntent % Dk Df products. A laminate material data 2.5 1x1080 57 3.63 0.0122 sheet should be used 4.5 1x2116 49 3.82 0.0114 as a guideline and 7.0 1x7628 40 4.06 0.0115 a comparison tool, 106 PP 75 3.25 0.0141 not a design tool. It 1080 PP 65 3.45 0.0131 is, however, often used for that purpose. The terms permittivity (Dk) and loss tangent (Df) are used on the data sheet to describe laminate electrical performance properties. Both of these properties vary with changes of resin content, temperature and moisture content of the substrate material.1,2 In addition to these factors, FiGurE 1. Variation of Dk and Df based the test methods that are used to evaluon resin content. ate the laminate properties can produce values that vary significantly. A standard which laminate is the right choice for the high Tg laminate data sheet states the application. “typical” electrical properties (Dk and Making an informed decision means Df), at 1 MHz to 1 GHz for one resin the designer should consider the variacontent. For high-speed digital substrates, tions in the material properties as well a data sheet will provide “typical” (not as the test methods used to develop the exact frequencies) data points for 2 GHz, material data, yet the typical data sheet 5 GHz and 10 GHz for one resin content. does not provide this type of detailed In some cases, the data sheet will specify information. As design requirements the test method that was used to test the for high-speed digital applications conmaterial. A PCB designer will need more tinue to push the envelope of perforinformation about the test methods used mance, it becomes critical to consider to prepare the laminate electrical data in these influences. order to make informed decisions about JANUARY 2009 PRINTED CIRCUIT DESIGN & FAB

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - January 2009

Printed Circuit Design & Fab - January 2009 Contents Our Line Market Watch Around the World Happenings ROI The Signal Doctor Positive Plating Final Finish Forum Making Sense of Laminate Dielectric Properties Design and Fab Tips for Improving Solder Mask Registration Automating the DDRx Interface Verification Process Printed Circuit Design & Fab Annual Buyers Guide: Special Suppliers Section Printed Circuit Design & Fab Annual Buyers Guide: Guide to Products and Services Off the Shelf Marketplace Ad Index BGA Bulletin

Printed Circuit Design & Fab - January 2009

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