PCB assembly cost: components, placements and everything the BOM does not show

Two things make this trade different from every other one covered here. The bill of materials usually **dominates** the cost — often several times everything else combined. And machine time does not track boards; it tracks **placements**, so two boards of the same size can differ several-fold in assembly cost.

The ten categories, in production order

1. Components — the bill of materials

Every line at the price you actually pay at your order quantity, not at a catalog price for a reel you will never buy. Include the bare board, and include parts fitted by hand.

Components not fitted must be marked as such rather than deleted — a BOM line that quietly disappears is indistinguishable from one that was forgotten, and six months later nobody can tell which happened.

2. Machine time — by placement, not by board

Placement machine time is proportional to the number of placements, so cost it that way. Reflow is different: an oven processes a board in a fixed time regardless of how many parts are on it, so it is costed per board, or per panel if you run boards in arrays.

Mixing the two into one "assembly rate per board" is what makes a dense board look cheap and a sparse one look expensive. Both errors are large.

3. Labor

Machine operation, hand placement, inspection, touch-up, functional test. Hand placement is the block that scales worst — a handful of odd-form parts can cost more labor than several hundred machine placements.

4. Consumables

Solder paste, solder wire, flux, stencil, nozzles, cleaning agents. Stencils are per design — divide by the boards the stencil will produce over its life, not by one order.

5. Scrap

Boards that fail and cannot be recovered. Value them at the stage they failed: a board that fails functional test has consumed every component plus all the assembly, which makes it one of the most expensive scrap events in any trade.

6. Rework

Replacing a component, reflowing a joint, correcting polarity. Almost every assembly line reworks something, so a zero here is unusual — if it is genuinely zero, enter zero rather than leaving it blank.

7. Outside processing

Conformal coating, potting, specialist test, programming, box build. Vendor price per lot divided by boards, plus transport both ways.

8. Packaging

Antistatic bags, trays, moisture barrier, desiccant, humidity indicators. Not optional in this trade — the packaging is part of what keeps the product functional, so it is the wrong place to trim without measuring.

9. Freight

Light, high value. Cost by shipment divided by boards; insurance is worth a separate line here because the goods are worth far more than they weigh.

10. Plant overhead

Space, static control, humidity control, dry storage for moisture-sensitive parts, supervision. Dry storage is a real recurring cost that only this trade carries, and it belongs here rather than nowhere.

Three checks

1. Component prices are at your order quantity, not catalog price.
2. Placement time is by placement; reflow time is by board or panel.
3. Hand-placed parts are costed as labor, not folded into machine time.