Lè frekans segondè/mikwo ond radyo frekans siyal la manje nan Pkb kous, pèt la ki te koze pa kous la tèt li ak materyèl la sikwi pral inevitableman jenere yon sèten kantite chalè. Pi gwo pèt la, pi wo pouvwa a pase nan materyèl PCB la, ak pi gwo chalè a pwodwi. Lè tanperati fonksyònman nan kous la depase valè nominal la, kous la ka lakòz kèk pwoblèm. Pou egzanp, MOT nan paramèt fonksyònman tipik, ki se byen li te ye nan PCB, se tanperati a opere maksimòm. Lè tanperati fonksyònman an depase MOT la, pèfòmans ak fyab sikwi PCB la ap menase. Atravè konbinezon an nan modèl elektwomayetik ak mezi eksperimantal, konprann karakteristik sa yo tèmik nan PCB mikwo ond RF ka ede evite degradasyon pèfòmans sikwi ak degradasyon fyab ki te koze pa tanperati ki wo.

Konprann ki jan pèt ensèsyon rive nan materyèl sikwi ede pi byen dekri faktè enpòtan ki gen rapò ak pèfòmans tèmik sikui PCB wo-frekans yo. Atik sa a pral pran sikwi liy transmisyon microstrip la kòm yon egzanp pou diskite sou konpwomi ki gen rapò ak pèfòmans tèmik kous la. Nan yon sikwi microstrip ak yon estrikti PCB doub-sided, pèt gen ladan pèt dielectric, pèt kondiktè, pèt radyasyon, ak pèt flit. Diferans ki genyen ant eleman pèt diferan yo gwo. Ak kèk eksepsyon, pèt la flit nan sikui PCB segondè-frekans se jeneralman trè ba. Nan atik sa a, depi valè pèt flit la trè ba, li pral inyore pou moman sa a.

Pèt radyasyon

Radiation loss depends on many circuit parameters such as operating frequency, circuit substrate thickness, PCB dielectric constant (relative dielectric constant or εr) and design plan. As far as design schemes are concerned, radiation loss often stems from poor impedance transformation in the circuit or electromagnetic waves in the circuit. The difference in transmission. Circuit impedance transformation area usually includes signal feed-in area, step impedance point, stub and matching network. Reasonable circuit design can realize smooth impedance transformation, thereby reducing the radiation loss of the circuit. Of course, it should be realized that there is the possibility of impedance mismatch leading to radiation loss at any interface of the circuit. From the point of view of operating frequency, usually the higher the frequency, the greater the radiation loss of the circuit.

Paramèt materyèl sikwi ki gen rapò ak pèt radyasyon yo se sitou konstan dyelèktrik ak epesè materyèl PCB. Pi epè sikwi a, se pi gwo posiblite pou lakòz pèt radyasyon; pi ba εr nan materyèl PCB la, se pi gwo pèt radyasyon nan kous la. Konplètman peze karakteristik materyèl, yo ka itilize substrats sikwi mens kòm yon fason pou konpanse pèt radyasyon ki te koze pa materyèl sikwi ki ba εr. Enfliyans epesè sikwi substrate ak εr sou pèt radyasyon sikwi se paske li se yon fonksyon ki depann de frekans. Lè epesè substra sikwi a pa depase 20mil ak frekans fonksyònman pi ba pase 20GHz, pèt radyasyon sikwi a ba anpil. Piske pi fò nan modèl sikwi ak frekans mezi nan atik sa a pi ba pase 20GHz, diskisyon an nan atik sa a pral inyore enfliyans nan pèt radyasyon sou chofaj sikwi.

Apre inyore pèt radyasyon ki anba a 20GHz, pèt ensèsyon yon sikwi liy transmisyon mikrostrip sitou gen ladan de pati: pèt dielectric ak pèt kondiktè. Pwopòsyon de la sitou depann sou epesè substra sikwi a. Pou substra mens, pèt kondiktè se eleman prensipal la. Pou plizyè rezon, li difisil jeneralman pou predi pèt kondiktè avèk presizyon. Pou egzanp, brutality sifas yon kondiktè gen yon gwo enfliyans sou karakteristik transmisyon onn elektwomayetik. Brutalizasyon sifas papye kwiv la pa pral sèlman chanje konstan pwopagasyon vag elektwomayetik nan kous mikrostrip la, men tou, ogmante pèt kondiktè sikwi a. Akòz efè po a, enfliyans nan brutality papye kwiv sou pèt kondiktè tou depann de frekans. Figi 1 konpare pèt ensèsyon nan sikui liy transmisyon 50 ohm microstrip ki baze sou diferan epesè PCB, ki se 6.6 mils ak 10 mils, respektivman.

The simulation results are obtained using Rogers Corporation’s MWI-2010 microwave impedance calculation software. The MWI-2010 software quotes the analytical equations in the classic papers in the field of microstrip line modeling. The test data in Figure 1 is obtained by the differential length measurement method of a vector network analyzer. It can be seen from Fig. 1 that the simulation results of the total loss curve are basically consistent with the measured results. It can be seen from the figure that the conductor loss of the thinner circuit (the curve on the left corresponds to a thickness of 6.6 mil) is the main component of the total insertion loss. As the circuit thickness increases (the thickness corresponding to the curve on the right is 10mil), the dielectric loss and the conductor loss tend to approach, and the two together constitute the total insertion loss.

The circuit material parameters used in the simulation model and the actual circuit are: dielectric constant 3.66, loss factor 0.0037, and copper conductor surface roughness 2.8 um RMS. When the surface roughness of the copper foil under the same circuit material is reduced, the conductor loss of the 6.6 mil and 10 mil circuits in Figure 1 will be significantly reduced; however, the effect is not obvious for the 20 mil circuit. Figure 2 shows the test results of two circuit materials with different roughness, namely Rogers RO4350B™ standard circuit material with high roughness and Rogers RO4350B LoPro™ circuit material with low roughness.

For thinner substrates, the use of smooth copper foil can significantly reduce the insertion loss. For the 6.6mil substrate, the insertion loss is reduced by 0.3 dB due to the use of smooth copper foil at 20GHz; the 10mil substrate is reduced by 0.22 dB at 20GHz; and the 20mil substrate, the insertion loss is only reduced by 0.11 dB.

This means that when the circuit is fed with a certain amount of RF microwave power, the thinner the circuit will generate more heat. When comprehensively weighing the issue of circuit heating, on the one hand, a thinner circuit generates more heat than a thick circuit at high power levels, but on the other hand, a thinner circuit can obtain more effective heat flow through the heat sink. Keep the temperature relatively low.

Yo nan lòd yo rezoud pwoblèm nan chofaj nan kous la, sikwi ideyal la mens ta dwe gen karakteristik sa yo: faktè pèt ki ba nan materyèl la sikwi, lis sifas kòb kwiv mete mens, ba εr ak segondè konduktiviti tèmik. Konpare ak materyèl la sikwi nan εr segondè, lajè a kondiktè nan menm enpedans la jwenn anba kondisyon an nan εr ki ba ka pi gwo, ki se benefisye diminye pèt la kondiktè nan kous la. Soti nan pèspektiv nan dissipation chalè sikwi, byenke pifò substra sikwi PCB segondè-frekans gen trè pòv konduktiviti tèmik relatif nan kondiktè, konduktiviti nan tèmik nan materyèl sikwi se toujou yon paramèt trè enpòtan.

Yon anpil nan diskisyon sou konduktiviti nan tèmik nan substra sikwi yo te elabore nan atik pi bonè, ak atik sa a pral site kèk rezilta ak enfòmasyon ki soti nan atik pi bonè. Pou egzanp, ekwasyon sa a ak Figi 3 yo itil pou konprann faktè ki gen rapò ak pèfòmans tèmik materyèl sikwi PCB yo. Nan ekwasyon an, k se konduktiviti tèmik (W/m/K), A se zòn nan, TH se tanperati sous chalè a, TC se tanperati sous frèt la, ak L se distans ki genyen ant sous chalè a ak sous frèt la.