PCB Assembly Cost Drivers and Quotation Inputs

An assembly price is the sum of a material cost, a process cost, a test cost and a yield allowance. The quotation is usually argued at the total, when the decisions that set it were made in the design.

What Drives the Material Cost

The bill of materials dominates the cost of most products. The drivers within it are the part count, the part technology and the sourcing channel rather than the individual prices.

A part that is available from several sources costs less than one that is not, and the difference is a design decision made at selection. Our component selection notes describe how availability enters the choice.

Board Cost

The board cost follows from the area, the layer count, the material, the finish and the tolerance class. The area and the layer count dominate, and both are set by the routing rather than by the function.

The panel utilisation is part of the same calculation: a board outline that fits a standard panel well costs less than one that leaves a large margin unused. Our panel design notes describe how the utilisation is raised.

Process Cost

The process cost is the number of steps multiplied by the time each takes. A board that needs two reflow passes, a selective solder operation, an underfill and a coating costs more than the sum of the individual operations would suggest, because each adds handling.

The component count and the placement rate set the machine time, which is usually the largest single process element on a high volume product.

Test Cost

The test cost is the fixture, the programming and the test time. The fixture and the programming are one off; the test time is per unit and it is where the recurring cost sits.

A test that takes a minute per board costs more over a production run than a fixture that costs several thousand. The trade should be made with the volume rather than with the unit price. Our test point notes describe the access that keeps the test time down.

Yield Allowance

The yield allowance is the cost of the boards and the components that are lost, plus the labour to find the failures. It is invisible in a quotation that quotes only a unit price.

A design that yields ninety percent costs more per good unit than one that yields ninety nine, even when the quoted process price is identical. Our yield notes describe how the figure is produced.

Volume Effects

The fixed costs are spread over the volume, so the unit cost falls steeply at first and flattens. The shape of that curve is why a prototype and a production build are priced differently rather than priced with a margin.

The volume also decides which processes are available: a stencil and a programmable placement program are justified at one volume and not at another.

Reducing the Cost

The reductions that matter are in the design: fewer parts, fewer layers, fewer process steps, a standard panel size and a test that can be shortened.

Where the reduction is requested after the design is released, the options are the ones that were available then, and the cost of the change is added to the saving. Our manufacturability review notes describe where the discussion belongs.

Process Control and Verification

On a design of this kind, quotation is the item that decides how the rest of the board is arranged. 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, quotation is the item that decides how the rest of the board is arranged. 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.

Process Control and Verification

On a design of this kind, quotation is the item that decides how the rest of the board is arranged. 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, quotation is the item that decides how the rest of the board is arranged. 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.

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

Why does the same design cost different amounts at different suppliers? Because the quoted price contains different assumptions about volume, yield, test time and the process steps that are included.

Is a lower layer count always cheaper? It reduces the board cost and it can increase the assembly cost if the routing forces a denser layout with a tighter pitch.

What does gopcb provide for cost analysis? We provide a breakdown into material, board, process, test and yield elements, panel utilisation and layer count review, process step and reflow pass reduction, test time and fixture trade analysis, and yield based comparison of design options.