How exactly to determine substrate materials of RF and Micro
2018-12-07 12:06Writer: qyadminReading:
As an early on stage in circuit design, PCB substrate materials selection performs such an integral role in RF/Microwave PCB design that ideal substrate material plays a part in excellent performance and high reliability of end products. When contemplating substrate materials in conformity with your PCB design, some aspects need to be concentrated like family member permittivity, reduction tangent, thickness, environment etc. The next content will fine detail their significance and ideal selection methods will be shown.
• Family member Permittivity
Comparative permittivity identifies the ratio between dielectric continuous and vacuum permittivity. Family member permittivity of substrate materials requested RF/Microwave PCB design must be sufficiently high to meet needs of space and weight. Other applications such as high-speed interconnect, however, demand extremely low comparative permittivity to create high-impedance circuits with suitable collection width and impedance tolerances.
Before last substrate materials dedication, some parameters need to be verified including range width for a certain selection of table thickness, wavelength of circuit working frequency and approximate sizes of leading components. A sketch of circuit panel diagram needs to be used order to determine appropriate maximum and minimal relative permittivity.
Moreover, family member permittivity deviation provided by substrate materials manufacturer needs to be low enough to make electric performance within a tolerance range.
• Reduction Tangent
Dielectric reduction is a function regarding reduction tangent and comparative permittivity. For some substrate materials, dielectric reduction per unit size may possibly be offset by software of shorter lines that can reduce conductor reduction as well, which is quite crucial when conductor reduction becomes apparent in high-frequency situation. Thus, when guidelines of component reduction in a few circuits are being approximated, it is reduction per unit duration or frequency that is approximated instead of regular loss per device line size under given frequency.
Within a certain frequency range, substrate materials loss needs to be low enough to be able to meet insight/result power requirements with warmth dissipation issues avoided. Furthermore, power response of some circuit elements (such as filters) must maintain a razor-sharp frequency roll-off feature so that electric performance necessity can be met. Normally, dielectric reduction can impact this frequency feature.
Substrate materials thickness is associated the next design elements:
a. Track width. To keep up given feature impedance, substrate materials thickness should be reduced to meet up with the requirement of track width reduce. High-impedance track on thin substrate materials perhaps needs extremely low track width as it pertains to manufacturing.
b. Mechanical Performance. Circuits built on unsupported slim substrate materials may bow, warp or distort, which won't possibly eventually rigid and thermoset materials.
c. Size Balance. Generally speaking, slim substrate materials perform worse than solid ones in conditions of size balance. Plus, slim substrate materials will also produce setbacks to producer or business lead to increased expense.
d. Cost. Generally, substrate materials that are thicker per device area are more expensive than the ones that are slim per device area.
electronic. Conformability. For circuit planks that are had a need to flex into simple bending designs such as cylinder or cone, slim boards can handle bending to lessen curvature radius with substrate materials or copper foil halted from being damaged.
f. Dielectric Break down. For parallel planks, thin dielectric materials features proportionally higher dielectric break down voltage than heavy material.
g. Power Managing Capability. Power managing capacity for high-frequency circuit planks are tied to two aspects that may be alleviated with the addition of substrate materials thickness. Similarly, high power can be partially dissipated through temperature. Alternatively, high-peak power level may lead corona inception to create electricity and reduce life time of substrate materials.
Printed circuit plank fabrication and functional environment keep constraints to substrate materials selection. The primary material performances that needs to be taken into account include:
a. Temperature Balance. Operational and specialized highest and cheapest temperature should be assured and temperature limit should be indicated as "maximum" or "constant". Electric performance customization should be calculated in peak temperature and weighed against design necessity. Circuit planks won't possibly be produced work through the selection of intermittent temperature peaks so "constant" temperature should be employed to estimation performance. Permanent harm occurred on mechanical performance of circuit table should be examined in "intermittent" limit temperature range.
b. Humidity Level of resistance and Chemical substance. Substrate materials should absorb low amount of humidity so that electric performance of circuit panel won't be certainly reduced in high-humidity environment. In the end, extra environmental safety solutions arouse extra production cost and design bargain. To-be-used techniques have to be compatible with chemical substance level of resistance and solvent level of resistance of substrate materials.
c. Anti-Radiation Performance. When RF/Microwave PCBs are applied in space or nuclear applications, substrate materials are affected from substantial ionizing radiation. Impact on substrate mechanical and electric performance by ionizing rays should be ensured and approximated. Furthermore, its accumulative impact should be ensured and effective procedure life-span of circuit plank should be weighed against that.
• Other Design Guidelines Regarding Substrate Material
a. Adhesion of copper coil must be high enough to withstand program and production environment in order never to cause permanent harm.
b. Comparative permittivity changes with temperature, that may possibly impact electric performance within working temperature range.
c. Reliability of surface attach devices (SMDs) and plated-through openings (PTH) is associated with CTE as well.
d. Thermal conductivity of substrate materials will impact design with thermal management concern considered.
electronic. When deciding casing and mounting, table warpage is highly recommended in advance.
f. Mechanical performance will most likely influence assembly and installation design.
g. Specific gravity of substrate materials determines weight of circuit panel.
h. Coefficient of thermal growth (CTE) needs to be carefully considered along the way of limit environment temperature and high-power components developing and app of reflow soldering or other high-temperature production.
i. Electrical resistivity is going to be an component associated with electric performance, particularly when high-impedance lines transmit high voltage, power amplification circuit, for example.