Repeat Order Assembly of an Industrial Robot Control Board

After a prototype has been verified, the usual next step is to order the same board again in a larger quantity. It looks like a matter of adding a zero to the quantity, but three things have often changed in between: part of the routing has been revised, a communication device has been replaced with a substitute, and the test programme has moved from a development version to a released one.

If the factory simply calls up the previous placement programme, the new board may be produced with the old coordinates. If the substitute was agreed in a message and never entered into the bill of materials, the next purchase may revert to the original part. A repeat order therefore starts by putting the hardware, the material, the placement programme, the programming file and the test requirement back under one revision.

Build a Change List First

For a repeat order the customer supplies this revision of the Gerber data, the bill of materials, the coordinates, the assembly drawing, the programme and the test description, and lists the reference designators that have changed relative to the previous batch. Items that have not changed are confirmed as unchanged rather than inferred from a file name, because two files with the same name can differ in content.

When an industrial robot control board is imported, the encoder interface, the communication transceiver, the controller, the power components and the direction sensitive devices are examined in particular. If the panel, the fiducials or a package has changed, the stencil and the machine programme are re-evaluated rather than reused, because a panel that has been rearranged prints differently even when the board itself is unchanged.

Material left over from the previous batch does not go straight onto the line. The full part number, the packaging state and the applicable revision are verified, and material that has been withdrawn is removed from the stores and from the feeders so that it cannot be mixed with the new batch.

The First Article Is More Than Joints

After the first board has been built, the paste condition is checked from the print data, and optical inspection confirms the position, the orientation and the visible joints. The encoder connector, the communication interface and the heavier devices are examined for their placement height and their state after reflow, because those are the parts that determine whether the later tests can pass.

The release then extends to the programme and the interface. The customer provides the programming file, the device type, the interface definition and the method by which the revision is read back, and the test side is defined as the low voltage supply, the encoder simulation, the communication link and the acceptance conditions.

If the placement looks correct and the communication test fails, the possibilities are the programme revision, the interface connection, the crystal, the communication device and the soldering, and the answer is found by examining those in order. Concluding immediately that the placement is at fault is a diagnosis made before any evidence has been collected.

Managing the Anomaly Boundary During Volume

During volume assembly, a reference designator that raises repeated optical alarms causes the line to stop while the paste, the placement coordinates, the component packaging and the machine recognition are checked. When the failures are concentrated in one period of production, the programme, the material and the repair records for that period are used to narrow the scope, since a shared symptom usually has a shared cause.

Where a substitute has to be introduced mid-run, the board number or the batch at which the change begins is stated. Old and new material are not allowed to occupy the same production state, because if a fault appears afterwards the affected range can no longer be determined.

A repaired board repeats the appearance check, the programming check and the interface test before release. Boards that have passed, boards awaiting review and boards under repair are kept in separate flows so that a board that has not been retested cannot enter the delivery area.

What Is Delivered

What leaves the factory is a board together with a set of correspondences: this board revision with this programme revision, tested to this procedure, with these results. The record states the hardware revision, the programme revision and the test state to the customer’s requirement, and where the product carries tall connectors the packing is arranged in layers so that the interfaces are not loaded in transit.

The service covers placement, through hole parts, programming and interface testing. Where a repeat order is being prepared, sending the current production files together with the change list allows the remaining material, the stencil, the machine programme, the quantity and the date to be checked together, so that the answer to whether the order can go straight to the line is based on the data rather than on an assumption. Our industrial PCBA group handles this kind of order and PCBA testing covers the interface verification, with the records held under quality management.

Why a Repeat Order Is Not Automatic

The assumption that a repeat order carries no engineering is the source of most of the problems that appear in one. A revision change that is not announced, a substitute that is not recorded, a programme that was updated without the test being updated with it, or a stencil that has been in use for several batches and is no longer in the condition it was, all produce a result that differs from the previous batch while every document looks familiar.

The check that prevents them is short. Comparing the current revision against the previous one, confirming the material, and verifying the programming and test revisions takes less time than investigating a batch that has already been built to the wrong data.

What the Line Needs Before It Starts

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A repeat order runs efficiently when the material is complete on the day the line is free, and that requires the bill of materials to be confirmed early enough for purchasing to act. Long lead time parts are identified at the moment the order is placed rather than when the line is ready, and where a part has become difficult to obtain, the substitute is proposed and approved while there is still time to validate it.

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The stencil is the second item. A stencil that is stored between orders is checked before use, because a stencil that has been cleaned repeatedly or stored without support can lose the tension that the aperture design assumes. Where the stencil has reached the end of its life, making a new one at the start of the order is cheaper than discovering it during the run.

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The third item is the programme. The placement programme is generated from the current data, and the programming file for the device is verified against the revision the customer intends to ship. Where the customer has changed the firmware but not the test, or the test but not the firmware, the mismatch shows up as failures that look like process faults.

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Finally, the acceptance condition is confirmed. A test that was agreed informally for a prototype has to be written down for a volume order, with the supply, the interface, the steps and the pass criteria, so that the second shift reaches the same conclusion as the first.

FAQ

Can a previous programme be reused? It is re-generated against the current data, because a revision change that is not visible in the file name will otherwise be produced with the old coordinates.

Does leftover material go straight back on the line? It is rechecked for part number, packaging state and revision before it is released to production.

What confirms a batch is ready to ship? The hardware revision, the programme revision and the test state, recorded together, with the boards that were repaired retested against the same procedure.