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FREQUENTLY ASKED QUESTIONS LTCC VENDORS Answers National Semiconductor's Process December 1998.
General Notes: frequently asked question that follows very comprehensive intended help customer adequately assess National Semiconductor LTCC vendor.
General Questions/Requests: provide design guide soon possible? have document, Physical Design Guidelines that including file attachment this reply. This guideline defines design approach that will provide lowest cost commercial, high volume products. Deviations from these guidelines permitted extent identified following comments added cost. provide revenue breakdown space, commercial (what sectors medical, automotive, wireless) military? Currently, business commercial telecommunications products. have provided products past mass storage (disk drive) business automotive customers. manufacturing line originally developed military products such produced many qualified LTCC packages substrates MCMs microwave active array antennas. subsidiary larger company, publicly held private company? National Semiconductor publicly traded company. your customers? telecommunications area targeting larger wireless communications users such Motorola, Ericsson, Nokia, Nortel etc. Some customers have requested that disclose working relationships NDA. company LTCC manufacturing done National based company. LTCC manufacturing done provide chip wire assembly test both overseas.
Ceramic Structure: What material systems does DuPont, Ferro, Heraeus)? primarily DuPont also provide products, have built parts, Ferro Heraeus systems. Over what frequency range would recommend each system? Dupont Heraeus materials suitable applications through L-band. Above GHz, dielectric losses become significant either Ferro DuPont recommended. What advantages/disadvantages each system? DuPont demonstrated most consistent properties experience. They tend have more complete conductors, resistors etc. that compatible with their system. Ferro most success band above applications somewhat difficult process. DuPont system excellent microwave properties according measurements used building production quantities. Heraeus expected good contender lowest cost high volume. properties comparable DuPont 951. What largest size substrate accomplished date with each system (#layers, size, #vias)? DuPont been used build parts layers. Similar sized parts have been built using Ferro Herraeus lower volumes. maximum count layer been over 12,000. What minimum maximum tape thickness? minimum tape thickness available production mils (fired) while thickest tape approximately mils fired. Multiple dielectric layers used provide thicker fired layer dimension. have worked with 2-mil tape developmental programs this qualified production.
What issues/limitations arise producing large substrates larger)? currently have automated system parts. equipment process parts would semi-automatic equipment. What relationship involving number layers, ceramic size number, shape size cavities? general, cavities provided cost "empty volume cavity represents materials that paid discarded during manufacturing process. Deep, multilevel cavities most costly produce. Cavities with thin bases thermal arrays difficult build have flat bases. Cavities that have walls near edge ceramic part will require sawing size after firing which adds additional significant costs part. What issues/limitations arise large number cavities within ceramic structure densities order cavities within ceramic area)? total area cavities should less that substrate area. size cavities more important this example that absolute number. Cavities should similar size distributed uniformly avoid distortion fired part. cavities placed both sides ceramic what limitations/issues? currently recommend designs with sided cavities. cavities shape? Yes, sharp acute corners problem. Proper corner radius needed manufacturability. hermeticity ceramic been assessed? LTCC materials used National used build packages that will pass standard tests hermaticity. Have bonded ceramic metal what size metals have used? have build packages with LTCC with bonded seal rings heat spreaders mechanical backing plates. largest metal bonded ceramic date been 3.5" 1.5' seal rings approximately same dimensions. What recommended packaging options integration next higher assembly small large ceramic structure? This depends next level assembly structure. general, compliant interconnect most reliable least expensive solution. Flex cables, brazed soldered leads, ribbon wire bonds connectors have been used successfully. type connections parts larger that 0.5" 0.5" recommended high reliability, long life applications used noncritical stress environments. above features function material system used? Matching temperature coefficients between LTCC second level assembly improve reliability non-compliant connections.
Buried Passives: What material systems used they matched ceramic? buried conductors provide capacitor plates inductive functions. higher dielectric, available screen-printed dielectric internal laminate. Co-fired resistors available only surface integrated, buried components. What resistor inks available today development (range, tolerance, timeline developments) have done characterization tests? provide cofired resistors from ohms ohm. fired tolerances percent. Trimmed tolerances possible except very very high values. developing buried resistor capability. What capacitor inks available today development (series shunt models, range, tolerance, timeline developments) have done characterization tests? Interdigitated capacitors dual plate structures have been built with values multiple plate caps caps with high dielectric have been built values filter applications. tolerance typically simulation tools allow arbitrary plate configurations include "approximate" parasitic inductance model often predicted within although complex structures sometimes introduce sizable variations from this. 200. limit from dielectric loss about with standard dielectric conductor losses reduce this have capacitor composition that dielectric constant Characterization currently underway. What inductors have designed have done characterization tests? built number test inductors have measured data. have also developed simulation model that applicable very different inductor "shapes" (planar, multilayer, straight, spiral [round, square], meander, etc.). Inductors from have been built tested. inductance typically within within 10%. highest thus obtained about150 straight "resonators" Typical about predictable within 20%. What ferrites have been designed what characteristics? does currently work with ferrite tapes. aware sources ferrite tape materials that could develop there product need. What component tolerances expected versus positioning ceramic from outer perimeter center from layer bottom layer)? tolerance components based conductor patterns ceramic, e.g. capacitors inductors significantly affected position array. frame system tape handling during manufacturing that reduces tape distortion vision alignment system that minimizes layer layer misalignment achieve very repeatable products with limited variability across array. have capability trim components? routinely trims resistors that co-fired post printed surface LTCC. subcontract trim house located near facility this process. have demonstrated trimming capacitive stubs past microwave modules such process feasible LTCC.
Connectorization: Have provided interfaces? built both standard micro-BGA parts. attached miniaturized coaxial connectors ceramic structure? Yes, connectors. Have attached vertical horizontal leads ceramic structure? Yes, have attached clip lead, lead frames LTCC with solder braze.
Thermal Issues: What thermal conductivity ceramic? Various measurements under different conditions show thermal conductivity base ceramic vary between Watts/mK depending upon dielectric system under measurement. What your thermal dissipation methodology? There methods that work practice; thermal arrays under heat producing part. This robs routing area provide significant improvement typically Watts/mK. opening ceramic heat spreader. This also eliminates routing area under component provide best thermal management. Doesn't work flip chips course expensive brazing needed achieve hermaticity. using metal bonded ceramic, what limitations result (methodology, size limitation, temperature range, mismatch, test results) answer Question B.12. good results bonding metal stiffeners package brazing done degrees subsequent soldering operations brazed structures possible. LTCC varies material system generally low, around ppm/degree Metals used braze LTCC should match this. Cu/W composites Kovar alloys good choices.
Dielectric Characteristics: What range dielectric constants ceramic available? standard DuPont dielectric dielectric constant over frequency range GHz. Ferro standard dielectric dielectric constant while loss DuPont material dielectric constant 7.3. developing printed dielectric film local higher capacitance components with 60-80. What frequency response dielectric constant from GHz? This difficult answer lines. sending some typical curves DuPont along with videotape. What loss tangent ceramic frequency dependence over frequency range from GHz? Same above What nature dielectric constant i.e. isotropic anisotropic? Anisotropic plane. What temperature coefficient dielectric constant i.e. variation dielectric constant ppm/deg have measured reported about 50ppm/C Does dielectric constant ceramic vary with time i.e. aging effects? aware aging effect with standard dielectric. There appears measurable Curie temperature effect. What tolerance dielectric constant? Approximately What coefficient thermal expansion (CTE) ceramic? varies with material. typically ranges between over ppm/C with tolerance What density ceramic? DuPont material gm/cc.
Conductor Characteristics: What inks have buried layers, surface vias? National typically uses pure silver buried conductor traces highest conductivity lowest cost. surface, silver alloys doped with inhibit metal migration adverse environments. also provide gold pads wirebonding; compositions suitable both wire available. Copper metallization available some systems post fired metallization required. conductors' inks matched ceramic? conductor inks closely matched ceramic. some cases, must provide gridded patterns large areas metallization distribute metal within layers best structural stability. What electrical conductivity conductors? Buried silver conductors vary from milliohms /square. Pd/Ag conductors have resistivity more used only solder pads outside part. Gold metallization provide conductivity similar pure silver course much more expensive used routing. cost effective when used small amounts wire bond pads. What thickness conductor traces buried layers surface? Buried conductors typically microns fired thickness. Thicker layers provided will introduce distortion used extensively. Surface conductors also similar thickness buried layers. Have characterization tests been done traces? Yes, data characteristics that share with customers. What standard line width what limitations line widths lower than standard? have standard target line width mils provide printed lines down mils. This adds cost smaller dimension should used sparingly. recently developed photo-imageable conductor with DuPont under DARPA contract that allows provide line spaces with thicknesses comparable printed conductors. What metallization compatibility between conductor inks i.e. barrier materials required (e.g. Ag)? Barrier metals required between pure conductors. conductors interface both heavily doped with interface will appear consistent pure metal film these interfaces have been used Military systems with high reliability. What process compatibility conductors wire bonding, soldering, epoxy bonding? conductors that have excellent properties wirebonding. Pure bonding doped bonding available. Pd/Ag conductor compositions being used solder connections with excellent results through National's standard reliability testing procedures filled epoxy works well with Pd/Ag conductors reliable over long term high temperature, thermal cycle humidity testing.
Quality: What quality standard support i.e. ISO, IPC, MIL-STD? National Semiconductor sites ISO9001 certified Norske Veritas (DNV). LTCC facility audited ISO9001 23-24 September 1997, granted certification. periodical assessment performed 18-19 June 1998 with certification continuing. Various standards specifications used performing testing inspection routines including IPC-M103 MIL-STD-883, MIL-PRF-38534. What process controls applied during manufacture? Various process controls established LTCC starting with over process specifications workstation instructions entire operation including design, quality, manufacturing, inspection test. addition, along with tracking implemented critical points throughout manufacturing test areas. Operator training certification each process well documented established throughout entire operation. What test capability have mechanical tests, thermal tests electrical tests?
Testing capability currently includes thickness measurement, dimensional accuracy, wire bond, component shear, pull test, solderability, temperature cycling, continuity shorts testing, testing regimes. What your qualification heritage i.e. what environmental conditions have ceramic structure been exposed what were characteristics ceramic (size, #layers, etc.)? Qualification heritage included Un-bias Humidity, High Temperature Storage, Temperature Cycling, wire bond component shear, solderability, various packages with mixed layer metals layers thickness
Processing Capability: provide complete fully populated assemblies (die installed etc.)? Yes, both wirebond capability engineering production levels. have flip-chip capability? subcontract assembly partners that have flip chip capability. National developed flip chip processing prime contractor under recent DOD/DARPA funded multiyear program.

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