Spare Parts Management for PCB Production

Spare parts management decides how long a machine stays down. Every board shop has a store room full of parts that are never used and a short list of parts whose absence stops the line, and the difference between the two is rarely reflected in the way the store is organised. The work is to identify the parts that matter, hold them in proportion to the lead time and the consequence of failure, and keep the record accurate enough to be trusted at two in the morning.

Which Parts Are Critical

A critical spare is one whose absence stops production and whose replacement cannot be obtained quickly. That definition has two parts, and both matter. A cheap sensor with a two week lead time can be more critical than an expensive motor that a local supplier stocks, and a part that is used on three machines is more critical than one used on a single lightly loaded machine.

The list should be built with the maintenance team and reviewed against the failure history. Parts that have failed more than once belong on it, and so do parts that are unique to a machine with no alternative route. Parts that can be improvised, substituted or borrowed from a redundant machine usually do not, and putting them on the list wastes the limited space and cash that the store has available.

Stock Control and Lead Time

The quantity to hold follows from the lead time and the consequence. A part that takes six weeks to arrive and stops the line needs more than one on the shelf, while a part available next day needs none at all if the supplier is reliable. The calculation is not complicated, but it requires the lead time to be recorded, which is where most stock control systems are weakest. Recording lead times should be part of the purchase process, and it should be corrected whenever an order arrives late.

The record should also carry the usage. A part used twice a year with a two week lead time may be held in a quantity of one, while the same part used monthly with the same lead time needs a small buffer. Without usage data the stock level becomes a matter of opinion, and opinions in a store room tend to grow into piles. Most stores hold far too much of what is cheap and convenient and far too little of what is long lead time and awkward to buy.

Keeping the Record Accurate

An inaccurate stock record is worse than no record, because it produces confidence without substance. The failure mode is predictable: a part is taken without being booked out, the record still shows one available, and the machine waits for a replacement that was expected to be on the shelf. Every store has this problem at some point, and the fix is to make booking out easier than not booking out.

The practical measures are a single clearly marked location for each part, a simple booking method that takes seconds, and periodic cycle counting rather than an annual stocktake. Counting a small section every week finds discrepancies while they are still small, and it also keeps the store tidy, because someone is looking at each shelf in turn with a reason to.

Supporting Maintenance Planning

Maintenance planning depends on parts being available at the scheduled time. A window that is opened for a task whose parts have not arrived is a window that will be wasted, and after two or three of those the schedule loses credibility. Checking the parts before confirming the window is a small discipline with a large effect on whether the maintenance programme survives.

The link should work in both directions. The maintenance schedule tells the store what will be needed in the coming weeks, and the store tells the planner what is on hand. Where the two are connected by a simple weekly list, both improve: the store stops buying what nobody needs and the planner stops scheduling work that cannot be completed.

Part Availability in Practice

Part availability is the property that decides how a breakdown ends. When the part is on the shelf the repair is a matter of hours, and when it is not the repair becomes a negotiation with a supplier whose delivery date is uncertain. The difference between the two situations is worth a great deal of money, and it is created long before the breakdown by a decision about what to keep on the shelf. That decision is easier to make calmly than under pressure, which is the argument for reviewing the critical list on a schedule rather than after an incident.

Availability also depends on knowing what the part is. A machine whose components are recorded with manufacturer part numbers is far easier to support than one whose parts are known only by description, because the number can be searched, cross referenced and ordered from any supplier. Building that record takes time at the start and saves days at the end, and it is the reason Bills of materials for equipment are worth maintaining.

Obsolescence and Storage

Parts become obsolete, and a store accumulates items for machines that were sold years ago. The list should be reviewed periodically and items for retired equipment removed, or the store will slowly fill with material that has no possible use and will hide the parts that do. Space is the constraint in most store rooms, and the parts that matter need to be findable. A store that is full of obsolete material is a store that takes ten minutes to find a fuse.

Storage conditions matter for some items. Electronic assemblies, belts, seals and adhesives all have shelf lives or environmental sensitivities, and a part that has degraded in storage can fail immediately when fitted, which is more frustrating than the original failure. Date labelling at goods in and a first in first out rule prevent most of this.

Practical Rules

Identify the critical spares from the failure history, set the stock level from the lead time and the usage, and make booking out easier than not booking out. Keep the record of the equipment and its parts accurate, and check availability before confirming a maintenance window.

Review the list once a year, remove what belongs to retired equipment, and store sensitive items with dates so that the oldest stock is used first. Spare parts management is not glamorous work, but it is the difference between a breakdown that costs an afternoon and one that costs a week, and in a shop that measures itself on delivery and quality that difference is visible on the bottom line.

FAQ

Which spares should always be held? Parts that both stop production and cannot be obtained quickly. Long lead time items used on the bottleneck machine are the clearest cases.

How is stock level decided? From the lead time, the usage rate and the consequence of a stoppage. Reliable next day supply needs almost no stock.

Why do stock records go wrong? Usually because booking out is slower than not booking out. A single location and a fast method fix most of it.