Before the Batch Starts: Material Allowance, First Article and Review

Most of the difficulty in a first batch is decided before it starts, and the decisions are small ones: how much material to buy, what will be checked before the run continues, and whether the design has been read by anyone who understands manufacture. Each of them takes minutes to settle and each of them has a cost attached if it is left open.

A small batch is where this matters most, because there is little redundancy in the order. A shortage of a dozen components on ten thousand boards is an inconvenience; on fifty boards it stops the run, and the same is true of a design detail that nobody examined.

The Material Allowance and Why It Exists

Assembly consumes more parts than the number of boards requires. Parts are lost during setup and feeder changes, damaged during adjustment, and consumed while the process is being established for the product. The allowance exists to cover that, and it is normally expressed as a percentage added to the calculated requirement.

The percentage is not uniform. Small passives and parts that have to be hand-placed incur more loss than large devices supplied in tubes; a new product incurs more than one that has been built before; and a design with a device that has to be re-fed several times incurs more than a straightforward one.

Under-providing is the more expensive mistake. Where the material is short at the machine, the options are to wait for a delivery, to build part of the batch or to substitute a part that may not be approved. All three cost more than the surplus would have, and the surplus is usually returnable or reusable on the next order.

The First Article Before the Run Continues

The first article is the confirmation that the data, the material and the process have produced what was intended: the right device, in the right position, in the right orientation, with a joint that has formed correctly.

Its value depends on when it happens. Verified before the batch continues, it prevents an error from being repeated across the whole order. Verified after, it becomes a description of what went wrong.

On a small batch the first article also carries a large share of the quality assurance, because there are few units over which any other check can be spread. Where the board carries joints that cannot be seen, this is the natural point at which to apply the method that can see them, and the point at which the result is worth recording.

The DFM Review and What It Should Produce

A review of the design against what can be produced is the cheapest service in the whole order, because it happens before anything is built and its findings are used by every batch that follows.

What it should produce is a list of specific findings with their consequences: a footprint that does not match the package in the bill of materials, a connector specified by height without the mating side, a component too close to the break line, a test point that is missing from the layout, a pad geometry that the stencil cannot serve well.

A review that returns nothing on a first design is worth a question. Designs are rarely complete on the first pass, and the absence of findings is more often evidence that the data was accepted than that it was examined.

Packing, Delivery and the Customer’s Own Process

The last preparation concerns the delivery. Boards require protection from static, moisture and mechanical load, and the requirement depends on what will happen to them afterwards: immediate assembly, a period in storage, or distribution to different projects.

Deciding that in advance is cheap. The packing method, the number of units per package, the labelling and the reference information can all be stated in the order, and each of them affects whether the boards can be used on arrival or have to be sorted first.

The Supplier Relationship and Why Continuity Pays

The assets that make a repeat order efficient are created during the first one: the stencil, the placement programme, the recorded process parameters and the inspection criteria. Where the same supplier builds the second batch, those still exist; where the supplier changes, they have to be recreated.

That is the practical argument for continuity, and it is stronger than any discount. A supplier who has built the product once knows where the difficulties are, what the last batch measured and how the material behaved, and the second order begins from that position rather than from the files.

It also changes the nature of the conversation. Questions become specific, because both sides have a shared reference, and the answers arrive faster for the same reason. The work involved is the familiar one: SMT assembly, verification through PCBA testing and the controls that keep each batch comparable under quality management.

What the Customer Should State in the Order

The information that prevents most of the avoidable difficulty fits into a short message, and it is worth sending in that form rather than spreading it across several conversations.

The revision that is to be built, stated explicitly where more than one exists. The bill of materials with the critical devices marked, the parts that may be substituted and the range within which substitution is allowed. The quantity, together with the allowance for attrition and who provides each part.

Then the requirements that follow the placement. Whether a programme has to be loaded and which version, what has to be verified and against which limits, whether a coating is applied and in what sequence relative to testing, and how the units are to be packed and identified.

Finally, the purpose of the boards. Whether they will be used for development, for a customer evaluation or for equipment that will run continuously determines the profile, the inspection and the packing, and it is the one item that a supplier cannot infer from the data.

When Each Item Has to Be Settled

The preparation is not a single task but a short sequence, and each item has a moment before which it must be decided.

The material allowance has to be settled before the purchase order is placed, because it changes the quantity that is bought. The review has to happen before the stencil is ordered, since its findings may affect the pad geometry. The first article happens after the boards and the material exist but before the batch continues. The packing requirement has to be known before the units are counted and boxed, and the test definition before the first unit is tested.

None of those moments is difficult to meet, and all of them are easy to miss when the order is placed quickly. The cost of missing one is not the rework of a single item but the additional week that a decision taken later imposes on the whole sequence.

FAQ

How much extra material should be provided? Enough to cover setup, adjustment and the loss typical of the components involved. Under-providing stops the run, while a surplus is usually usable on the next order.

When should the first article be checked? Before the remainder of the batch is built, so that any error is corrected once rather than repeated.

What does a good design review produce? A short list of specific findings with their consequences, rather than a statement that the data has been received.