Fixture Cleaning: Fixture and Tooling Cleaning and Maintenance

A fixture is a precision tool that is used every day and cleaned rarely. The material that builds up on it changes the height of the board and therefore the print, and the change is gradual enough to go unnoticed.

What Builds Up

Flux, paste, adhesive and dust collect on support pins, pallet faces and locating features. The deposit is soft at first and it cures with each pass through the oven.

The build-up changes the board height at the point of support. Our board support notes describe the consequence.

How It Alters the Process

A pallet face that has gained a layer of cured flux holds the board higher, which changes the print gap and the stencil contact. The print volume drifts and the drift is attributed to the paste.

The measurement that shows it is the print volume. Our SPI notes describe it.

Cleaning Methods

The method has to remove cured flux without damaging the fixture. A solvent that attacks an anodised surface or a plastic pin costs more than the deposit it removes.

The cleaning should be specified with the fixture. Our cleaning notes describe the chemistry selection.

Accuracy Checks

The fixture should be checked against a reference for flatness, pin height and locating position at a stated interval. The check is a measurement rather than a visual inspection.

Our calibration notes describe the traceability that goes with it.

Wear Items

Pins, springs, seals and locating bushes wear. They should be listed with a replacement interval rather than replaced when they fail.

The list belongs with the fixture record. Our floor control notes describe the arrangement.

Scheduling the Work

Cleaning and checks are planned into the production schedule rather than done when there is time. A fixture pulled out during a run costs a changeover and one pulled out at a planned break costs nothing.

Our changeover notes describe the planning that goes with it.

Verification

The verification is a cleaning method that does not damage the fixture, an accuracy check against a reference at a stated interval, a wear item list with replacement intervals, and a print volume trend that would show a drift.

Our quality notes describe how the records are kept.

Process Control and Verification

The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.

Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch. Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end.

Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed.

A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance.

Checks Before Release

The checks that matter are the ones performed on the product rather than on a sample kept for the purpose, because a coupon that travels with the panel is the only evidence about that panel. Where a requirement can be measured, it should be measured at the point of manufacture and recorded against the board or the lot it applies to.

A parameter that is set once and never re verified drifts, and the drift is usually discovered by a defect rather than by the record. The tooling, the material and the profile form one system, and a change to any of them should be assessed against the other two before it is released.

Where the process window is narrow, the measurement resolution has to be better than the window, or the data cannot distinguish a good part from a marginal one. A record that identifies the operator, the date and the settings is worth more than a record that identifies only the result.

The acceptance criteria should be written before the work starts, so that the decision is made by the specification rather than by the person inspecting.

FAQ

How often should a fixture be cleaned? It depends on the flux and the volume. The interval should be set from the print volume trend rather than from a guess.

Can a pallet be cleaned in the same machine as the boards? Sometimes, and the compatibility should be checked because the pallet may be too heavy or incompatible with the chemistry.

What does gopcb provide for fixtures? We provide a cleaning method specified with the fixture, an accuracy check against a reference at a stated interval, a wear item list with replacement intervals, and a print volume trend that shows a drift before it becomes a defect.