A solder-paste viscosity number should travel with the method that produced it. Receiving inspection and the supplier may obtain different values because their temperatures, instruments or measurement sequences differ. Establish comparability before deciding that a shipment is unsuitable for printing.
Retrieve the complete measurement condition
IPC-TM-650 2.4.34.2 defines a spiral-pump procedure with controlled preparation, temperature and shear conditions. It also addresses agreement when other equipment is used. A bare viscosity value omits information needed to apply that procedure meaningfully.
Identify the exact paste formulation, alloy, powder designation and package. Confirm that the receiving requirement refers to that product variant. A specification copied from another paste in the same family can produce a misleading rejection.
Compare the two laboratory records
| Field | What to reconcile |
|---|---|
| Method | Procedure and revision |
| Equipment | Sensor or adapter and instrument configuration |
| Temperature | Sample conditioning and measurement state |
| Preparation | Mixing and loading sequence |
| Shear condition | Selected speed and reporting point |
Retain the original units and any conversion. If the instrument produces a trend, keep the trend with the selected result rather than saving only the final displayed number. It can help the laboratories determine whether the required measurement state was reached.
Investigate the sample history
Separate an unopened receiving sample from paste recovered from a printer. Both may be worth studying, but they answer different questions. Record storage, warming, opening and prior processing so a worked sample is not described as the original supplied material.
If a common-method retest is needed, agree on sample identity, preparation and reporting before testing. Preserve enough material for a supplier comparison when practical. Repeating a measurement with undocumented changes makes the disagreement harder to resolve.
For example, an incoming result taken under one instrument configuration should not be corrected by an informal multiplier derived from a single unrelated paste. Any correlation used for acceptance needs an agreed basis that represents the intended materials and range.
Include the person responsible for resolving method differences in the receiving plan. Production should know whether a pending comparison means the lot is held, conditionally released or awaiting a specific additional test; an unexplained numerical mismatch should not become an informal operator decision.
Connect the result to print performance
A viscosity check supports material control, but it does not independently qualify every aperture or printing condition. Review representative deposits and the actual process when deciding whether a material change affects production.
Document whether the outcome is a confirmed material difference, a method discrepancy or an unresolved result requiring further evidence. Avoid changing the paste specification solely to make two incompatible reports agree.
The slump-test guide addresses a separate paste behavior, while stencil separation trials connect material behavior to the print operation.
Move from reading to a build-ready project
Use the fabrication and assembly checklists to prepare drawings, production files and test requirements.
Open the DFM checklist