Nuair a thèid an comharra tricead rèidio tricead / microwave a thoirt a-steach don PCB cuairteachadh, bidh an call a dh ’adhbhraicheas a’ chuairt fhèin agus an stuth cuairteachaidh gu cinnteach a ’gineadh beagan teas. Mar as motha an call, is ann as àirde an cumhachd a bhios a ’dol tron ​​stuth PCB, agus mar as motha an teas a thèid a chruthachadh. Nuair a tha teòthachd obrachaidh a ’chuairt nas àirde na an luach a tha air a mheas, faodaidh an cuairteachadh cuid de dhuilgheadasan adhbhrachadh. Mar eisimpleir, is e am paramadair obrachaidh àbhaisteach MOT, a tha aithnichte ann am PCBan, an teòthachd obrachaidh as àirde. Nuair a bhios an teòthachd obrachaidh nas àirde na MOT, bidh coileanadh agus earbsachd a ’chuairt PCB ann an cunnart. Tro bhith a ’cothlamadh de mhodaladh electromagnetic agus tomhas deuchainneach, faodaidh tuigse air feartan teirmeach PCBs microwave RF cuideachadh le bhith a’ seachnadh truailleadh dèanadais cuairteachaidh agus truailleadh earbsachd air adhbhrachadh le teòthachd àrd.

Tha a bhith a ’tuigsinn mar a tha call cuir a-steach a’ tachairt ann an stuthan cuairteachaidh a ’cuideachadh le bhith a’ toirt cunntas nas fheàrr air na factaran cudromach co-cheangailte ri coileanadh teirmeach cuairtean PCB àrd-tricead. Gabhaidh an artaigil seo an cuairteachadh loidhne tar-chuir microstrip mar eisimpleir gus beachdachadh air na buannachdan co-cheangailte ri coileanadh teirmeach a ’chuairt. Ann an cuairteachadh microstrip le structar PCB le dà thaobh, tha call a ’toirt a-steach call dielectric, call stiùiriche, call rèididheachd, agus call aodion. Tha an eadar-dhealachadh eadar na diofar phàirtean call mòr. Le beagan ach a-mhàin, tha call aodion de chuairtean PCB àrd-tricead glè ìosal. San artaigil seo, leis gu bheil luach call aoidionachd gu math ìosal, cha tèid mothachadh dha aig an àm seo.

Call rèididheachd

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.

Tha na paramadairean de stuthan cuairteachaidh co-cheangailte ri call rèididheachd sa mhòr-chuid seasmhach dielectric agus tiugh stuth PCB. Mar as tiugh an t-substrate cuairteachaidh, is ann as motha a tha e comasach call rèididheachd adhbhrachadh; mar as ìsle εr an stuth PCB, is ann as motha a bhios call rèididheachd na cuairt. A ’tomhas feartan stuthan gu h-iomlan, faodar cleachdadh fo-stratan cuairteachaidh tana a chleachdadh mar dhòigh air call rèididheachd adhbhrachadh le stuthan cuairteachaidh ìosal. Tha buaidh tighead substrate cuairteachaidh agus εr air call rèididheachd cuairteachaidh air sgàth gu bheil e na ghnìomh a tha an urra ri tricead. Nuair nach eil tiugh an t-substrate cuairteachaidh nas àirde na 20mil agus tha an tricead obrachaidh nas ìsle na 20GHz, tha call rèididheachd a ’chuairt gu math ìosal. Leis gu bheil a ’mhòr-chuid de mhodalan cuairteachaidh agus tricead tomhais san artaigil seo nas ìsle na 20GHz, bidh an deasbad san artaigil seo a’ seachnadh buaidh call rèididheachd air teasachadh cuairteachaidh.

An dèidh a bhith a ’seachnadh call rèididheachd fo 20GHz, tha call cuir a-steach cuairteachadh loidhne tar-chuir microstrip sa mhòr-chuid a’ toirt a-steach dà phàirt: call dielectric agus call stiùiriche. Tha cuibhreann na dhà gu mòr an urra ri tiugh an t-substrate cuairteachaidh. Airson fo-stratan nas taine, is e call stiùiriche am prìomh phàirt. Airson mòran adhbharan, mar as trice tha e duilich ro-innse a dhèanamh air call stiùiriche. Mar eisimpleir, tha buaidh mhòr aig garbhachd uachdar stiùiriche air feartan tar-chuir tonnan electromagnetic. Bidh garbh uachdar foil copair chan ann a-mhàin ag atharrachadh gluasad iomadachaidh tonn electromagnetic den chuairt microstrip, ach bidh e cuideachd a ’meudachadh call stiùiriche a’ chuairt. Air sgàth buaidh a ’chraicinn, tha buaidh garbhachd foil copair air call stiùiriche cuideachd an urra ri tricead. Tha Figear 1 a ’dèanamh coimeas eadar call cuir a-steach de chuairtean loidhne tar-chuir microstrip 50 ohm stèidhichte air diofar thiugh PCB, a tha 6.6 mils agus 10 mils, fa leth.

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.

Gus fuasgladh fhaighinn air duilgheadas teasachaidh a ’chuairt, bu chòir na feartan a leanas a bhith aig a’ chuairt tana tana: feart call ìosal den stuth cuairteachaidh, uachdar tana copar rèidh, εr ìosal agus giùlan teirmeach àrd. An coimeas ris an stuth cuairteachaidh àrd εr, faodaidh leud an stiùiriche den aon bhacadh a gheibhear fo chumhachan εr ìosal a bhith nas motha, a tha buannachdail gus call stiùiriche a ’chuairt a lughdachadh. Bho shealladh sgaoileadh teas cuairteachaidh, ged a tha seoltachd teirmeach glè ìosal aig a ’mhòr-chuid de shubstridean cuairteachaidh PCB àrd an coimeas ri luchd-stiùiridh, tha seoltachd teirmeach stuthan cuairteachaidh fhathast na paramadair glè chudromach.

Chaidh mòran de chòmhraidhean mu ghiùlan teirmeach fo-stratan cuairteachaidh a mhìneachadh ann an artaigilean roimhe, agus bidh an artaigil seo a ’togail cuid de thoraidhean agus fiosrachadh bho artaigilean roimhe. Mar eisimpleir, tha an co-aontar a leanas agus Figear 3 feumail gus tuigse fhaighinn air na factaran co-cheangailte ri coileanadh teirmeach stuthan cuairteachaidh PCB. Anns a ’cho-aontar, is e k an seoltachd teirmeach (W / m / K), is e A an sgìre, is e TH teothachd an stòr teas, is e TC teothachd an stòr fuar, agus is e L an astar eadar an stòr teas agus an stòr fuar.