Wakati mawimbi ya masafa ya juu/mawimbi ya mawimbi ya redio yanapoingizwa kwenye PCB mzunguko, upotevu unaosababishwa na mzunguko yenyewe na nyenzo za mzunguko bila shaka zitazalisha kiasi fulani cha joto. Kadiri upotevu unavyozidi, ndivyo nguvu inayopita kwenye nyenzo ya PCB inavyoongezeka, na ndivyo joto linalozalishwa zaidi. Wakati joto la uendeshaji la mzunguko linazidi thamani iliyopimwa, mzunguko unaweza kusababisha matatizo fulani. Kwa mfano, parameter ya kawaida ya uendeshaji MOT, ambayo inajulikana katika PCB, ni joto la juu la uendeshaji. Wakati joto la uendeshaji linapozidi MOT, utendaji na uaminifu wa mzunguko wa PCB utatishiwa. Kupitia mchanganyiko wa vielelezo vya sumakuumeme na vipimo vya majaribio, kuelewa sifa za joto za PCB za microwave za RF kunaweza kusaidia kuepuka uharibifu wa utendaji wa mzunguko na uharibifu wa kutegemewa unaosababishwa na joto la juu.

Kuelewa jinsi hasara ya kuingizwa hutokea katika nyenzo za mzunguko husaidia kuelezea vyema mambo muhimu yanayohusiana na utendaji wa joto wa nyaya za juu-frequency PCB. Makala haya yatachukua mzunguko wa laini ya upokezaji wa mikrostrip kama mfano ili kujadili utendakazi wa hali ya joto wa saketi. Katika mzunguko wa microstrip na muundo wa PCB wa pande mbili, hasara ni pamoja na kupoteza dielectric, hasara ya conductor, hasara ya mionzi, na kupoteza kuvuja. Tofauti kati ya vipengele tofauti vya kupoteza ni kubwa. Isipokuwa chache, upotezaji wa uvujaji wa saketi za PCB za masafa ya juu kwa ujumla ni mdogo sana. Katika makala hii, kwa kuwa thamani ya kupoteza uvujaji ni ya chini sana, itapuuzwa kwa muda.

Kupoteza kwa mionzi

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.

Vigezo vya vifaa vya mzunguko vinavyohusiana na upotezaji wa mionzi ni mara kwa mara ya dielectric na unene wa nyenzo za PCB. Uzito wa substrate ya mzunguko, uwezekano mkubwa wa kusababisha hasara ya mionzi; chini ya εr ya vifaa vya PCB, hasara kubwa ya mionzi ya mzunguko. Uzito wa sifa za nyenzo kwa kina, matumizi ya substrates za saketi nyembamba zinaweza kutumika kama njia ya kumaliza upotezaji wa mionzi unaosababishwa na vifaa vya chini vya εr. Ushawishi wa unene wa substrate ya mzunguko na εr juu ya kupoteza mionzi ya mzunguko ni kwa sababu ni kazi inayotegemea mzunguko. Wakati unene wa substrate ya mzunguko hauzidi 20mil na mzunguko wa uendeshaji ni wa chini kuliko 20GHz, hasara ya mionzi ya mzunguko ni ndogo sana. Kwa kuwa mifano mingi ya mzunguko na masafa ya kipimo katika makala hii ni ya chini kuliko 20GHz, majadiliano katika makala haya yatapuuza ushawishi wa kupoteza mionzi kwenye joto la mzunguko.

Baada ya kupuuza upotevu wa mionzi chini ya 20GHz, hasara ya kuingizwa kwa mzunguko wa mstari wa maambukizi ya microstrip hasa inajumuisha sehemu mbili: kupoteza dielectric na kupoteza conductor. Uwiano wa hizo mbili hasa inategemea unene wa substrate ya mzunguko. Kwa substrates nyembamba, hasara ya conductor ni sehemu kuu. Kwa sababu nyingi, kwa ujumla ni vigumu kutabiri kwa usahihi hasara ya kondakta. Kwa mfano, ukali wa uso wa kondakta una ushawishi mkubwa juu ya sifa za maambukizi ya mawimbi ya umeme. Ukwaru wa uso wa foil ya shaba hautabadilisha tu wimbi la uenezi wa wimbi la umeme la mzunguko wa microstrip, lakini pia kuongeza upotezaji wa kondakta wa mzunguko. Kwa sababu ya athari ya ngozi, ushawishi wa ukali wa foil ya shaba kwenye upotezaji wa kondakta pia hutegemea frequency. Kielelezo cha 1 kinalinganisha upotevu wa uwekaji wa saketi 50 za laini za upitishaji za mikrostrip kulingana na unene tofauti wa PCB, ambao ni mil 6.6 na mil 10, mtawalia.

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.

Ili kutatua tatizo la kupokanzwa kwa mzunguko, mzunguko mwembamba unaofaa unapaswa kuwa na sifa zifuatazo: sababu ya chini ya hasara ya nyenzo za mzunguko, shaba laini ya uso nyembamba, chini ya εr na conductivity ya juu ya mafuta. Ikilinganishwa na nyenzo za mzunguko wa high εr, upana wa conductor wa impedance sawa iliyopatikana chini ya hali ya chini ya εr inaweza kuwa kubwa, ambayo ni ya manufaa kwa kupunguza hasara ya conductor ya mzunguko. Kutoka kwa mtazamo wa utaftaji wa joto la mzunguko, ingawa substrates nyingi za mzunguko wa juu wa PCB zina conductivity duni ya mafuta ikilinganishwa na makondakta, conductivity ya mafuta ya vifaa vya mzunguko bado ni parameter muhimu sana.

Majadiliano mengi kuhusu conductivity ya mafuta ya substrates ya mzunguko yamefafanuliwa katika makala za awali, na makala hii itanukuu baadhi ya matokeo na taarifa kutoka kwa makala za awali. Kwa mfano, equation ifuatayo na Kielelezo 3 ni muhimu kuelewa mambo yanayohusiana na utendaji wa joto wa vifaa vya mzunguko wa PCB. Katika equation, k ni conductivity ya mafuta (W/m/K), A ni eneo, TH ni joto la chanzo cha joto, TC ni joto la chanzo cha baridi, na L ni umbali kati ya chanzo cha joto na chanzo cha baridi.