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54 The PCB Design Magazine • May 2015 III. Calculated Data 1. Polyimide (85N resin/E-Glass reinforce- ment) at 1 MHz (Figure 3 and 4). 2. Thermally conductive epoxy (92ML res- in / E-Glass reinforcement) at 1 MHz (Figure 5 and 6). 3. Multiclad HF (MultiClad resin / E-Glass reinforcement) at 10 GHz (Figure 7 and 8). In order to maintain the specification toler- ance of dielectric constant around the nomi- nal 3.7, the resin weight percentage needs to be controlled to approximately 80%+/- 0.75%. While this will vary slightly by glass style, the overall system is designed to produce laminates that fall within dielectric constant tolerance of 3.7 +/- 0.06. 4. Polyimide / Nonwoven Aramid (85N res- in / NWA reinforcement) at 1 MHz (Figure 9). Note that with the nonwoven aramid (NWA) reinforced products, the key to consistent per- formance is CTE control, therefore the resin content is held at a specification value of 49% for all three basic thicknesses of the NWA rein- forcement so that the effective CTE is the same for all laminate thicknesses and PWB builds. IV. Consequences of Material Choices With most resin systems, the largest impact of varying resin content is the change in intrin- sic properties such as dielectric constant and CTE which are mathematically dependent on the resin content and the physical properties of the material. As a result of modifying resin con- tent, CTE and Dk move in opposite directions. While this is obvious when we look at the data, it is something that many do not understand intuitively. It's important that designers associ- ate the choice of resin content, desired thick- ness, etc., with the results they will obtain. In general when the resin content increases, several things occur in consequence: Figure 3. Figure 5. Figure 4. Figure 6. article THE COMPOSITE PROPERTIES OF RIGID VS. MuLTILAyER PCBS continues