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- Before opening: verify the material and route
- Mix to restore uniformity without adding air
- Do not standardise a universal thinning ratio
- Control the first prints before running the lot
- Manage the paste while it is on the screen
- Dry, cure, or fire according to the material system
- Inspect the finished film before releasing the route
- Close the container and the record
Prepared by Chipsimple Engineering Team, Engineering and technical content review
Published online August 9, 2026 · Reviewed August 9, 2026
Source and scope: This guide combines company-engineer notes from November 2021 and January 2025. A source-specific low-temperature paste data set is treated as an example—not as a house-wide specification. Always follow the released product data sheet, safety data sheet, traveller, and drawing.
Most silver-paste defects are not created by one dramatic mistake. They accumulate: a cold container opened too early, a rough mixing tool, ten extra minutes uncovered, a small unrecorded solvent addition, a screen left idle, and an oven loaded differently from the qualification run. A usable work instruction controls that sequence from receipt to close-out.
Before opening: verify the material and route
Match the product code and lot to the traveller or material list. Confirm expiry, seal, storage history, and the substrate and cure route for the job. Polymer silver ink, air-fired ceramic conductor, and silver-filled adhesive may look related but are not substitutes. Check that the correct screen, squeegee, fixtures, cleaning materials, and test coupon are ready before exposing the paste.
If the container has been stored cold, condition it sealed for the specified time. Opening a cold container can introduce condensation. If the product is specified for room-temperature storage, do not refrigerate it by habit.
Mix to restore uniformity without adding air
Use a clean, compatible, burr-free spatula or the approved mixer. Fold material from the bottom and walls into the body at the specified speed and time. Avoid whipping. Air bubbles can create print voids, and aggressive shear or heating can change a structured paste.
Some settling is explicitly allowed by certain supplier data sheets. A hard heel, gel, skin, foreign material, or dried fragments need a hold decision. Do not push questionable particles through the screen and expect the screen to act as a filter.
Do not standardise a universal thinning ratio
The older engineer note included dilution ratios. Those can be valid only for the exact formulation, solvent, print method, and approved procedure from which they came. They should not be published as general silver-paste advice. Solvent addition changes solids, rheology, deposit thickness, levelling, drying, adhesion, and electrical performance.
Many commercial pastes are supplied ready to print. DuPont 7095 states that adjustment should not normally be needed and permits its specified thinner only for solvent-loss replacement or slight print adjustment. KA801 names another approved thinner and notes that thinning may be desired for some printing requirements. Neither statement authorises an arbitrary shop solvent.
Control the first prints before running the lot
Print a setup coupon or first article with the released screen and settings. Check image completeness, edge definition, bridging, pinholes, contamination, registration, and the required wet, dry, or fired geometry. Record paste temperature, room conditions, screen identity, squeegee, pressure, speed, snap-off or peel settings, and elapsed time.
Use the minimum approved paste volume that maintains a stable flood and print. Avoid allowing paste to dry in low-flow screen regions. If the machine stops beyond the documented pause, use the restart or screen-clearing rule rather than simply increasing pressure.
Manage the paste while it is on the screen
Track time on screen and replenishment. Keep the paste covered where the process allows. Add only traceable material from the same allowed lot strategy. Never return dried edge material, cleaner-contaminated material, or unknown screen scrap to the original container.
Watch trends across the run: line width, deposit thickness, incomplete openings, surface texture, and resistance. A gradual drift can signal solvent loss, screen blockage, paste warming, squeegee wear, or substrate variation. Trend evidence is more useful than a late adjustment made after final inspection.
Dry, cure, or fire according to the material system
Drying removes solvent before the next operation. Curing develops a polymer-bound functional film. Firing removes organics and develops a sintered inorganic film. The words are not interchangeable. Record actual process time, temperature, airflow or atmosphere, belt speed where applicable, loading, fixture, and part orientation.
The source note cited an example polymer silver paste with 65–70% solids, a stated Brookfield viscosity, PET or PVC substrates, and an 80 °C dry route. Those figures describe that example formulation and measurement method. They cannot be used for a polyimide paste cured near 200 °C or a ceramic paste fired above 500 °C.
Read these fields as a set
| Composition properties | Solids, density, viscosity method, thinner, and coverage are linked; none should be copied without its test condition. |
|---|---|
| Printing | Substrate treatment, mesh, emulsion, equipment, levelling, and deposit thickness define the supplier’s example route. |
| Thermal process | Box oven, conveyor, infrared, or firing profile must produce the required part temperature and film state without damaging the substrate. |
| Finished properties | Resistance, adhesion, hardness, flexibility, chemical resistance, and operating limit are meaningful only with their specimen and method. |
| Storage and safety | Temperature, shelf life, seal, conditioning, clean-up, ventilation, PPE, and disposal belong to that product and its SDS. |
Inspect the finished film before releasing the route
Electrical resistance is essential but not sufficient. Depending on the drawing, check width, spacing, thickness, adhesion, flexibility, hardness, continuity, isolation, surface condition, pad quality, and registration. For a flexible circuit, include bending or forming where relevant. For a contact track, include contact resistance, wear, and environmental exposure. For a sensor, verify the functional curve.
Use a retained reference or control coupon when it helps detect gradual material or process change. Keep raw readings with lot and process traceability.
Close the container and the record
- Remove contamination from the sealing surface without dropping dried material into the paste.
- Close the lid immediately and return the material to its specified storage condition.
- Record open time, quantity used or returned, screen time, any authorised adjustment, and remaining quantity.
- Segregate recovered paste if the procedure allows recovery; never merge unknown histories.
- Dispose of wipes, solvent, and paste residues through the approved waste stream.
Stable printing comes from repeatable handling. The operator should not need to recreate formulation work at the machine.
Primary references
- DuPont Kapton KA801 Polyimide Silver Conductor data sheet — one complete example of composition, screen printing, cure, storage, mixing, thinner, clean-up, and safety references.
- DuPont BQ131 Silver Conductive Composition data sheet — a contrasting polymer silver formulation with different substrate and drying conditions.
- DuPont 7095 Silver Conductor data sheet — fired-silver handling and processing guidance that demonstrates route separation.
Set the handling route from the drawing and material data
Send the substrate, printed geometry, electrical target, thermal limit, assembly sequence, environment, quantities, and required evidence. The material and work instruction can then be reviewed together.