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50 The PCB Design Magazine • February 2016 When fabricators are choosing a material, they are normally familiar with the bonding materials that are appropriate for their circuit construction. The electrical performance is not always critical, but when it is, the fabricators may not completely understand how the ma- terial can impact the material electrical perfor- mance. The following is an overview of differ- ent bonding materials used in high-frequency multilayer PCB applications. The materials used to bond high-frequen- cy multilayers may differ greatly in their for- mulations. Many of these bonding materials are glass-reinforced; however, there are several commonly used bonding materials which are not woven glass-reinforced. The non-reinforced bonding materials are typically a thermoplastic polymer film, however there are some excep- tions. Woven glass-reinforced bonding mate- rials are usually thermoset systems and often with special filler to enhance the high frequen- cy performance properties. The thermoplastic bonding materials are brought to a melt temperature during lamina- tion to achieve adhesion of the layers for the multilayer circuit. These materials can also re-melt after the multilayer has been adhered and re-melting can cause delamination which is why it is typically avoided. The lamination melt temperature and the cautionary re-melt temperatures vary with the type of thermoplas- tic bonding materials. Some fabricators may not have the equipment necessary to reach these higher temperatures necessary for lamination of a multilayer PCB. The re-melt temperature is typically a concern for the processes following the lamination, which exposes the circuit to el- evated temperatures such as soldering. by John Coonrod rogers corporation Multilayer PCB Bonding Materials for High-Frequency Applications lightning speed laMinates 50 The PCB Design Magazine • February 2016

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