Thick-Film Paste Families and Selection Guide

Source and scope: This guide consolidates two overlapping Chinese notes written by company engineers in January 2025. The English edition corrects one important ambiguity in the source: tungsten and molybdenum–manganese metallization pastes are refractory conductor systems, not ordinary resistor pastes. Supplier data and a released process specification remain controlling.

“Electronic paste” is a useful shop-floor term, but it is too broad for a drawing or purchase specification. Two grey pastes can require different substrates, atmospheres, peak temperatures, print thicknesses, and downstream finishes. One may become a resistive film on fired alumina; another may form a refractory conductor inside a co-fired ceramic package. Selecting by colour, metal name, or nominal viscosity is not enough.

Classify the paste by the job the fired or cured layer must do

The first division is functional. A conductor paste creates current-carrying tracks, electrodes, terminations, or vias. A resistor paste creates a controlled resistive element whose sheet resistance, TCR, voltage coefficient, stability, and trim behaviour matter. A dielectric paste provides electrical insulation, crossovers, multilayer separation, or a barrier on metal. An overglaze protects a printed feature or supports trimming and environmental performance. Adhesion promoters, solder barriers, carbon contacts, and other specialty compositions solve narrower interface problems.

These names describe a function, not a universal chemistry. A silver conductor formulated for polyester cannot be substituted for an air-fired silver conductor on alumina. A dielectric qualified under one conductor may blister, crack, or change adhesion when paired with another. A resistor family designed for a particular conductor and overglaze should be evaluated as that material stack.

Separate fired ceramic pastes from polymer thick-film inks

Conventional fired thick film compositions use an organic vehicle to carry functional powder and, where applicable, glass or other inorganic binders through printing. Drying removes volatile material. Firing then removes remaining organics and develops the functional film and its bond to the ceramic. Standard alumina systems are often discussed around an 850 °C air-fire route, but the exact profile belongs to the selected family and cannot be inferred from that shorthand.

Polymer thick-film materials work differently. Conductive or resistive particles remain in a cured polymer binder on PET, polyimide, FR-4, glass, or another approved substrate. Cure temperature is lower, and adhesion, flexibility, chemical resistance, sheet resistance, and maximum operating temperature are governed by that polymer system. “Silver paste” therefore does not tell an engineer whether the part must be fired or cured.

Refractory metallization is a separate design branch

Tungsten and molybdenum appear in high-temperature co-fired ceramic structures because their thermal processing and expansion behaviour can be matched to the ceramic package route. Kyocera describes tungsten conductors printed on green ceramic tape, laminated, and co-fired above 1500 °C in a controlled atmosphere for one high-alumina package process. That example is not a temperature instruction for post-fired thick film circuits; it illustrates why the route must be identified before a paste is discussed.

Mo–Mn metallization is commonly used to prepare ceramic surfaces for subsequent nickel plating and brazing. CoorsTek’s metallized-ceramics literature, for example, identifies a molybdenum–manganese thick-film layer followed by nickel plating for its specified alumina route. The original engineer note correctly points to refractory-metal particle control and ceramic bonding, but its high-temperature values must stay attached to the specific refractory system—not be transferred to ruthenium-oxide resistor paste or polymer silver ink.

Use substrate and final attachment as selection gates

The substrate narrows the viable families. Alumina grade, AlN grade, glass, stainless steel with a dielectric stack, LTCC tape, PET, polyimide, and FR-4 do not present the same surface chemistry or thermal budget. Surface finish, roughness, porosity, flatness, and previous layers also influence wetting and adhesion.

Then work backward from assembly. A soldered terminal needs a conductor and finish that retain solderability and adhesion through the assembly profile. A wire-bonded pad needs the released metallization and surface finish for the chosen wire and bond process. A wiper track needs wear and contact-noise validation. A heater stack needs dielectric integrity and a thermal design. A brazed ceramic feedthrough belongs to another branch again.

Do not promote typical data into a universal specification

Mesh count, emulsion thickness, viscosity, dried thickness, fired thickness, peak temperature, dwell time, and sheet resistance in a supplier data sheet describe the supplier’s test route. They are valuable starting points, but they are not cross-family constants. Heraeus product pages show this clearly: its AB1 silver conductor for glass, TC7404 Ag/Pd LTCC termination, and IP9117 alumina dielectric use different screens, temperatures, and functional targets.

The same caution applies to the 0.0127 mm coating thickness and sub-2 µm particle statements in the Chinese source. Those may describe a particular formulation or process target. They should not appear on a public page as guaranteed values for every tungsten or Mo–Mn paste without the material specification and test method that produced them.

Information needed before a paste route can be released

• Electrical function of every printed layer and the required values at defined conditions.
• Substrate material, grade, thickness, surface condition, dimensions, and thermal limit.
• Layer order, conductor interfaces, via or crossover construction, and complete firing or curing sequence.
• Attachment method: solder, braze, wire bond, conductive adhesive, pressure contact, or wiper.
• Operating temperature, voltage, current, power, humidity, fluids, mechanical load, and required life tests.
• Appearance, dimensional, electrical, adhesion, insulation, and traceability records required for release.

A paste is not selected in isolation. The releasable unit is the substrate, printed stack, thermal route, assembly interface, and inspection plan.

Primary references

1. Heraeus Electronics, Thick Film Materials portfolio — functional paste categories and paste-specific processing data.
2. CoorsTek, Metallized Ceramics for Electronic Applications — a manufacturer example of Mo–Mn metallization and nickel plating on specified ceramics.
3. DuPont 6444 Dielectric technical data sheet — an example showing that dielectric properties and processing are tied to substrate and compatible conductors.