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RF & WirelessTable 2: Examples of worldwide foundry servicesThis should bring the fields ofapplications closer to the reader.There are 4 main LTCC materialsystem suppliers available onthe market. The authors definesystems as set of unfired ceramictape available in different thicknessand with different permittivities.Each LTCC tape needsits own set of conductor pastes(this often includes resistor andcapacitor pastes) for the screenprinting process. The shrinkageproperties of the pastes arematched to the ceramic tapes.There fore conductors (resistorsand capacitors respectively) aredistinguished between inner andouter printing as well as fillingvia thru-holes. Special alloys areavailable for soldering and bondingcontact pads. However, themain ingredients of conductorpastes is gold and silver.Such LTCC material systems,which are qualified for RF applications,are offered by DuPont(951 and 943: low loss tape),Ferro (A6M: microwave tape,A6S: low cost microwave tape),Heraeus (CT700, CT800 andCT2000) and Electro-ScienceLaboratories (ESL). Other LTCCtapes are available on the market.Some of them have to be usedwith conductor pastes from oneof the previous mentioned suppliers.This is for instance CeramTecand Nippon ElectricalGlass (NEG).LTCC foundry services arespread all over the world. Thesefoundries offer the production ofmodules and circuits made ofstandard LTCC from DuPont,Ferro, Hereaus, ESL or their ownsupplementary ceramic tape. Thein-house LTCC solution couldrise the problem, that a secondsource for the production is notavailable, which might be animportant factor to launch a producton the market. Table 2 listsa selection of worldwide foundryservices for LTCC modules andgives an impression about theapplied tape materials and theproduction capabilities (as far asthese information could be foundout). Beyond these foundries anumber of companies have itsown LTCC production facilities,which are not available forcustomers.Bosch, Hitachi and Murata aretypical firms, who manufacturetheir own LTCC products for theautomotive, mobile communicationand consumer electronicmarkets.LTCC manufacturingprocessThe manufacturing steps formultilayer LTCC starts with thepreparation of the unfired ceramictape and is finished withthe inspection of the completedmodule. This process, which issimilar at all facilities, is illustratedin figure 1. The followingsection describes the manufacturingsteps with the example ofIMST’s sample and prototypeproduction line. The process isorganized to be compatible tomost of those foundry services,which utilize the unconstrainedsintering method.The green or unfired LTCC foilis delivered on a roller or as couponsin pre-confected sizes. Thefoil from the roller will be cut tofit into the manufacturing equipment(3.5 inch by 3.5 inch forIMST). In the next step the tapewill be processed under a YAGlaser,which is also used to trimresistors. The laser cuts 4 positionholes in each corner and anadditional one for the orientationof the coupon into the tape.A layout tool reads all cavitiesand vias from the layer’s artworkand implements the position andshape coordinates into a softwarecode, which controls the lasercutting. The dust from the laserburning is exhausted to keep thetape’s surface clean of particles.In volume production punchingof vias and cavities is preferred.Special punching machines withseveral tools in parallel shootsome ten thousand holes perminute into the tape. However,the laser cutting method is veryflexible (arbitrary shapes of cavitiesand different diameters forvia holes) and cheaper for prototyping,which results in thesame quality.In the next manufacturing stepthe vias will be filled with conductorpaste. This is done witha screen printer: a stainless steelstencil with the same via holeslike the tape is aligned abovethe ceramic. A doctor blade issqueezing down the paste thruthe stencil into the via, while avacuum pump below the porousnest helps to fill the via with the68 hf-praxis 9/2015