What is Stripline and microstrip line in PCB?
Tag# RT/duroid 5880 Tag# Rogers 5870
Rogers RT/duroid 5870 and 5880 glass microfiber reinforced PTFE
composites are designed for exacting stripline and microstrip
circuit applications.
Today we’re learning what stripline and microstrip line are.
Stripline: a banded line that walks in the inner layer and is buried inside
the PCB, as shown below
The brown part is the conductor, the green part is the PCB
insulating dielectric, stripline is the ribbon wire embedded
between the two layers of conductors.
Because stripline is embedded between two layers of conductors, its
electric field distribution is between two conductors (planes) that
wrap it, and does not radiate energy or be disturbed by external
radiation. but because it is all surrounded by dielectric
(dielectric constant is larger than 1), the signal is transmitted
slower in stripline than in microstrip line!
Microstrip line: a strip line attached to the surface of a PCB layer, as shown
below
The brown part is the conductor, the green part is the PCB
insulating dielectric, and the brown block above is the microstrip
line.
The light green part is epoxy organic material.
Since one side of the microstrip line is exposed to the air (which
can form radiation around or be disturbed by radiation around it),
and the other side is attached to the PCB insulating dielectric,
the electric field formed by it is distributed in the air. The
other part is distributed in PCB insulating medium. Its outstanding
advantage is that the signal transmission speed in the microstrip
line is faster than that in the stripline.
Conclusion
1. Microstrip line is a banded wire (signal line) separated from
the ground plane with a dielectric. If the thickness, width, and
distance between the line and the ground plane are controllable,
its characteristic impedance is also controllable.
2. Stripline is a copper strip line placed in the middle of the
dielectric between two layers of conductive plane. If the thickness
and width of the line, the dielectric constant of the medium and
the distance between the two conductive planes are controllable,
then the characteristic impedance of the line is also controllable.
Impedance calculation of microstrip and Striplines:
a. microstrip line Z ={87/[ sqrt (Er+ 1.41)]} ln [5.98 H/(0.8 W+T)]
Among them, the W is the line width, the T is the copper thickness
of the line, the H is the distance from the line to the reference
plane, and the Er is the dielectric constant of the PCB plate
material. This formula must be applied at 0.1<(W/H)<2.0 and
1<(Er) to 15.
b. stripline Z =[60/ sqrt (Er)] ln {4H/[0.67π(T +0.8W)]}
Among them, the H is the distance between the two reference planes,
and the line is located in the middle of the two reference planes.
This formula must be applied in W/H<0.35 and T/H<0.25.
| RT/duroid 5870 Typical Value |
| Property | RT/duroid 5870 | Direction | Units | Condition | Test Method |
| Dielectric Constant,εProcess | 2.33
2.33±0.02 spec. | Z | N/A | C24/23/50
C24/23/50 | 1 MHz IPC-TM-650 2.5.5.3
10 GHz IPC-TM 2.5.5.5 |
| Dielectric Constant,εDesign | 2.33 | Z | N/A | 8GHz to 40 GHz | Differential Phase Length Method |
| Dissipation Factor,tanδ | 0.0005
0.0012 | Z | N/A | C24/23/50
C24/23/50 | 1 MHz IPC-TM-650 2.5.5.3
10 GHz IPC-TM 2.5.5.5 |
| Thermal Coefficient of ε | -115 | Z | ppm/℃ | -50℃to 150℃ | IPC-TM-650 2.5.5.5 |
| Volume Resistivity | 2 x 107 | Z | Mohm cm | C/96/35/90 | ASTM D 257 |
| Surface Resistivity | 3 x 107 | Z | Mohm | C/96/35/90 | ASTM D 257 |
| Specific Heat | 0.96(0.23) | N/A | j/g/k
(cal/g/c) | N/A | Calculated |
| Tensile Modulus | Test at 23℃ | Test at 100℃ | N/A | MPa(kpsi) | A | ASTM D 638 |
| 1300(189) | 490(71) | X |
| 1280(185) | 430(63) | Y |
| Ultimate Stress | 50(7.3) | 34(4.8) | X |
| 42(6.1) | 34(4.8) | Y |
| Ultimate Strain | 9.8 | 8.7 | X | % |
| 9.8 | 8.6 | Y |
| Compressive Modulus | 1210(176) | 680(99) | X | MPa(kpsi) | A | ASTM D 695 |
| 1360(198) | 860(125) | Y |
| 803(120) | 520(76) | Z |
| Ultimate Stress | 30(4.4) | 23(3.4) | X |
| 37(5.3) | 25(3.7) | Y |
| 54(7.8) | 37(5.3) | Z |
| Ultimate Strain | 4 | 4.3 | X | % |
| 3.3 | 3.3 | Y |
| 8.7 | 8.5 | Z |
| Moisture Absorption | 0.02 | N/A | % | 0.62"(1.6mm) D48/50 | ASTM D 570 |
| Thermal Conductivity | 0.22 | Z | W/m/k | 80℃ | ASTM C 518 |
| Coefficient of Thermal Expansion | 22
28
173 | X
Y
Z | ppm/℃ | 0-100℃ | IPC-TM-650 2.4.41 |
| Td | 500 | N/A | ℃ TGA | N/A | ASTM D 3850 |
| Density | 2.2 | N/A | gm/cm3 | N/A | ASTM D 792 |
| Copper Peel | 27.2(4.8) | N/A | Pli(N/mm) | 1oz(35mm)EDC foil
after solder float | IPC-TM-650 2.4.8 |
| Flammability | V-0 | N/A | N/A | N/A | UL 94 |
| Lead-free Process Compatible | Yes | N/A | N/A | N/A | N/A |
