The lead time of an assembled board is not one number. It is a chain, and the longest chain sets the date. This article describes the links, what lengthens them, and how to plan so that a schedule survives a surprise.
The four links
- Fabrication. Making the bare board.
- Parts. Buying and receiving every component.
- Assembly and test. Putting the parts on and checking the result.
- Shipping. Getting the boxes to you, including customs.
Fabrication and parts run side by side. Assembly starts when both are complete. Shipping starts when assembly and test are complete. So:
total time = longer of (fabrication, parts) + assembly and test + shipping
- Fabrication: the bare board.
- Parts: the longer of the two links in this picture, and the one that most often sets the date.
- The join: assembly waits for the later of the two.
- Assembly and test.
- Shipping: the courier leg.
- Customs sits inside shipping. A missing paper stops the box there.
A fast fabrication does nothing for you when one part takes weeks to arrive.
One late part does not delay one step; it moves everything after it.
- The plan: fabrication and parts end close together and assembly follows.
- The same order, with one late part.
- The wait is the amber stretch: the part, not the board, sets the date.
- Assembly and shipping move later by the same amount. The dashed outlines show where they were.
Fabrication
How long a bare board takes depends mostly on its layer count and on special processes. A simple two-layer board is the quickest; each added layer pair means another lamination cycle; blind or buried vias, via filling, impedance-controlled stack-ups and special materials each add time. If a special laminate is not in stock, the factory must order it, and that can set the date alone. Exact times depend on the supplier and the season: ask for the time for your own board, not a general figure.
Parts
This link causes most late orders. Things that lengthen it:
- Long lead-time parts. Microcontrollers, FPGAs, power parts, some connectors, crystals and custom parts can take weeks or months to come from the maker if no distributor holds stock.
- Stock that disappears between quote and order. A part in stock on the day of the quote may be gone when the purchase is made.
- Minimum order quantities and reel sizes. These do not lengthen delivery directly, but a part that is sold only in large packs can be harder to source in a small quantity.
- Unclear BOM lines. A line without a manufacturer part number or with a footprint that does not match will stop the buyer until you answer.
- Substitutions that need your approval. Each is a question, and each question waits for you.
- Moisture-sensitive parts that must be baked before use. This is a day of process, not of purchasing, but it is easy to forget.
Parts you supply yourself take the time they take to reach the factory. Send them early, labelled, and with a few spares.
Assembly and test
Assembly itself is quick compared with the other links: paste printing, placement and reflow of one board take minutes, and a small batch can be quick when everything is on the shelf. The work around it takes the time: loading and checking feeders, a first-article inspection, programming, a functional test, rework if something fails. Boards with parts on both sides pass the line twice; through-hole parts add a soldering step. See How boards are assembled.
Shipping
Express courier from China to most countries takes a few working days door to door. Customs clearance can add to that, particularly when documents are missing or the receiver's broker has questions. Read Shipping and importing boards before you order.
What makes an order slip
| Cause | Where it hits |
|---|---|
| File errors found late | Fabrication restarts, or a board is built wrongly |
| An engineering question that waits for your answer | The whole order waits |
| A part out of stock or end of life | Parts |
| A part with a long manufacturer lead time | Parts |
| A change after the order is accepted | Often restarts the chain |
| Failed test, rework | Assembly and test |
| Missing or wrong customs papers | Shipping |
| Holiday periods | Every link; Chinese New Year closes factories and suppliers for a longer time than most holidays |
How to plan
- Check the BOM for availability first. Before the board design is final, look up each critical part, and design in parts you can buy.
- Order the long parts early. If one part takes many weeks, ask for it to be bought as soon as you decide, even while the board is still being checked.
- Name alternates. Every approved alternate removes a possible question.
- Answer engineering questions the same day. This is the cheapest schedule saving there is.
- Freeze the design before ordering. A change after the order is accepted may mean a new board.
- Allow a margin. Plan with a few days of slack for shipping and customs, more around public holidays.
- Prototype with a small run, then build in volume. The first run teaches you what is wrong; plan time for a second one.
- Decide in advance who handles customs. If you are the importer, find your broker before the box ships.
Quick turn orders
A fast turn is possible when the files are clean, the parts are all in stock, and the board uses standard processes. It becomes impossible the moment a part must be ordered from the maker. If you need a board quickly, make that the first design constraint: standard stack-up, parts in stock, and a BOM ready before the board is.
How this shows up when you order here
We do not state lead times in articles, because they depend on the board, the parts and the season. An engineer confirms the schedule with the order. The limits and options in force are on the capabilities page. The 25 checks at upload find file problems before you pay, so that those do not cost you time later. Boards are shipped by DHL Express from Shenzhen.