Conveyor Vibration and Component Movement in Reflow

While the solder is molten the components rest in liquid metal. Any movement of the board at that moment moves the parts, and the movement does not have to be large to produce a defect.

Where the Vibration Comes From

The conveyor chain, the drive, the fan units and the equipment beside the oven all contribute. A fan that is out of balance produces a periodic excitation that the board responds to.

The response depends on the board and its support. Our board support notes describe the deflection that follows.

Defects It Produces

A part that drifts shows as an offset without a placement error. A part that is standing on one end is a tombstone, and one that has moved enough to touch a neighbour is a bridge.

The pattern across the board is the clue to the direction. Our defect troubleshooting notes describe the mapping.

Resonance and Board Size

A board has a natural frequency, and a large thin panel on a conveyor is closer to the excitation than a small stiff one. Where the two coincide the amplitude is amplified.

Supporting the board changes the frequency. Our warpage notes describe the stiffness that matters.

Profile and Time Above Liquidus

The exposure lasts as long as the solder is liquid, so a shorter time above liquidus reduces the window in which movement matters. That is one reason to keep the profile inside its allowance.

Our profile notes describe the measurement.

Machine Condition

A worn chain, a misaligned rail or a loose panel produces a periodic disturbance that is easy to measure and easy to overlook. A vibration measurement on the rail under load identifies it.

Our floor control notes describe the maintenance planning.

Reducing the Movement

Supporting the board, balancing the fans, keeping the profile tight and using a pallet where the assembly allows all reduce it. Each is verifiable.

Where the assembly is very sensitive, a pallet is the practical answer. Our thermal mass notes describe the profile that goes with it.

Verification

The verification is a vibration measurement on the rail under production load, a board supported to raise its natural frequency, a profile kept inside its allowance, and a defect pattern reviewed for a directional signature.

Our quality notes describe how the records are kept.

Additional Considerations for This Build

Practical attention to component movement pays for itself here, because it decides whether the finished board behaves as the drawing intended. Where the requirement is not stated on the fabrication drawing or in the assembly notes, the shop has to assume a default, and that default is rarely the value the design was simulated with. Stating component movement explicitly, together with the tolerance that applies, removes the assumption and keeps the result predictable from batch to batch.

Deliberate attention to tombstoning pays for itself here, because it decides whether the finished board behaves as the drawing intended. Where the requirement is not stated on the fabrication drawing or in the assembly notes, the shop has to assume a default, and that default is rarely the value the design was simulated with. Stating tombstoning explicitly, together with the tolerance that applies, removes the assumption and keeps the result predictable from batch to batch.

Process Control and Verification

On a design of this kind, vibration is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.

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.

Process Control and Verification

On a design of this kind, vibration is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.

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.

Process Control and Verification

On a design of this kind, vibration is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.

A first article check confirms that the process and the drawing agree on the points listed above, and that the coupon data supports the values used in the design.

Where a measurement falls outside the expected window, the sample is retained so that the cause can be established before the balance of the batch is released.

FAQ

Can vibration be seen in the profile? No. It is a mechanical effect and it is measured on the structure rather than on the thermal curve.

Does a heavier board move less? It responds differently rather than less, because its natural frequency is lower and it may be closer to the excitation.

What does gopcb provide against movement during reflow? We provide board support chosen to raise the natural frequency, a vibration measurement on the rail under load, a profile kept inside its allowance to shorten the liquid time, and a defect pattern review that looks for a directional signature.