A buyer moves a product from 5,000 units a year to a first batch of 200 and the quotation comes back at six to eight times the unit price. The assumption is usually that the supplier has added margin for a small order. Most of the gap is not margin. It is the part of the cost that does not divide by quantity.
This article breaks a low volume build into the blocks that scale and the blocks that do not, shows where the money actually sits below 500 units, and lists what to settle before the enquiry so the price comes back comparable.
Why the unit price falls so fast with quantity
Every order carries a set of one time costs: tooling, programming, first article, documentation, test fixtures and the engineering hours that go into releasing a build. Those costs are the same at 50 units and at 5,000. Spread over 50 boards they dominate the price; spread over 5,000 they disappear into the material cost.
| Cost block | At 100 units | At 5,000 units |
|---|---|---|
| Solder paste stencil and tooling | Charged once, visible in the price | Charged once, negligible per board |
| Line setup and feeder loading | One or two shifts for the lot | Same shift count over twenty times the output |
| Programming and first article | Full package for a small lot | Same package, absorbed |
| Test fixture | Often the largest single line | Amortised across the programme |
| Component material | Reel minimums leave excess stock | Consumed within the build |
| Labour per board | Higher, because handling repeats per lot | Lower, because the line runs unattended |
The blocks buyers underestimate
Component minimums and excess material
A 0402 resistor may be quoted on a full reel of 10,000. A build of 200 boards using 40 per board consumes 8,000, and the rest is either billed to the buyer, held as customer stock, or split with another order. The same applies to connectors, crystals and any part with a maker minimum. On a low volume programme this line often exceeds the assembly labour, and it is the first thing to negotiate: buy the surplus on the buyer's account, keep it as consigned stock for the next build, or accept a cut reel with a handling charge.
Panel utilisation
Board size decides how many units fit a production panel, and the panel decides how much of the material and machine time is wasted. A board that fits four per panel carries roughly twice the assembly cost of the same area that fits eight, because the line moves the same number of panels for half the output. Checking the panel drawing before release is worth more than any negotiation on labour rate.
Test strategy
A bed of nails fixture can cost more than the assembly of the whole first lot. Below a few hundred units, flying probe or a functional test with a universal interface usually wins, and a dedicated fixture only makes sense when the same board will be built repeatedly. The decision belongs in the enquiry, not after the quote.
| Test route | Tooling | Fits |
|---|---|---|
| Flying probe | Programming only | First lots and high mix work |
| Bed of nails ICT | Fixture per board revision | Repeat builds from a few hundred units |
| Functional test | Interface and harness | Small lots that need a system level check |
Change control during the build
Small lots are usually early builds, and early builds change. A part substitution, a revised BOM line or a late mechanical change forces new programming, a new stencil revision and a repeat of the first article. Each one is priced as a new setup. Freezing the BOM for the duration of the lot is the simplest quality improvement available to a buyer.
What a low volume build needs to go right
Price is only half the argument. A 200 unit lot has no room for a second attempt, so the first pass has to be complete.
- BOM and Gerber matched before release, with alternate parts accepted in writing rather than assumed.
- Long lead and discontinued lines identified at enquiry, not at kitting. A single 26 week part can move the ship date by half a year.
- First article approved against the drawing, with the measurement record kept for the lot.
- Traceability per board: lot of each component, date code, and the test record tied to the serial number.
- A stated plan for the surplus material and the reels left over from the run.
How SUPERB Assembly handles small and mixed lots
Superb Automation has supplied components and assembly since 2000, and low volume work runs on the same lines as production. Seven SMT lines handle 01005 parts up to 55 mm connectors at up to 40,000 placements per hour, with 3D SPI before placement, 3D AOI after reflow, and CT capable X-ray on hidden joints. Through hole, selective solder and wave solder sit in the same flow, so a mixed technology board does not travel between suppliers.
For a small lot the practical parts are the ones that remove fixed cost: programming and first article done once per revision, flying probe test where a fixture cannot be justified, functional test on a universal interface, and component sourcing that reports long lead and end of life lines at the quotation stage rather than at kitting. The quality system is ISO 9001, with ISO 13485 applied to medical builds and workmanship to IPC-A-610 Class 2 or Class 3 as the drawing states.
- PCBA workshop: lines, placement capability and inspection equipment.
- Order online: what the panel and stack up data has to contain.
- BOM cost guide: where excess material and part choice move the price.
- Box build: what changes when the lot ships as a finished unit.
Frequently asked questions
Is there a minimum order quantity?
Small lots are accepted, but the cost per board rises as the quantity falls, for the reasons above. The honest way to compare suppliers is to ask for the same board at 100, 500 and 2,000 units and read which cost blocks change.
Should the buyer supply the components?
Consigned parts remove the reel minimum problem and give control over the exact part number. They also move the traceability and the shortage risk to the buyer. On a first build, a mixed model often works best: buyer supplies the long lead and the high value lines, the assembly house supplies the rest.
How long does a first low volume build take?
Material dominates the schedule, not the line. With all parts in stock a small lot can be built within days of first article approval; with one part on allocation the same lot can wait months. That is why the material review belongs at the enquiry.
Next step
Send the BOM with quantities, the Gerber data, the assembly drawing and the test requirement, and state the yearly volume next to the first lot size. The reply separates the one time costs from the per unit costs, marks the lines with minimums or long lead time, and quotes the build with the test route that fits the lot rather than the one that fits a production programme.
