How to select laminate for Microwave RF PCB

The selection of Microwave RF PCB laminate should consider its dielectric properties first, but must also consider the types and thickness of surface copper foil, environmental adaptability, processability factors as well as cost problem.

1 The types and thickness of copper foil;

Currently the most commonly used of the copper foil thickness is 35 μm and 18μm. The thinner copper foil is easier to achieve high image precision, so the high precision Microwave RF PCB should choose copper foil no more than 18μm. If choose 35μm copper foil, the high image precision will make the manufacturability worse, and yield rate will be down accordingly.

Studies have shown that the types of copper foil also have influence on image precision. Currently there are two types of copper foils, which are rolled copper foil and electrolytic copper foil. Compare to electrolytic copper foil, rolled copper foil is more suitable to manufacture high precision image, so it's the priority to select laminate with rolled copper foil.

2 Environmental adaptation;

There is no problem for existing Microwave RF PCB laminate to sustain the standard requirements -55 ℃ ~ + 125 ℃ temperature range. But we should also consider two points: one is through holes plate copper or not will effect the choices of laminate, regarding the microwave rf PCBs with plated through holes, the bigger coefficient of heat expansion on Z axis of laminate, the higher possibility for plated through holes crack under the impact of high and low temperature. So under the premise of meeting the dielectric properties, we should choose the laminate with small coefficient of thermal expansion on Z axis.

The second is the influence of humidity on the selection of microwave rf pcb laminate, resin in base laminate itself has very low water absorption, but after adding reinforced material, it will increase its overall water absorption obviously, it will also have influence on the dielectric properties if used in high humidity environment, so we should select laminate with low water absorption.


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