Who this section is for
Two readers arrive at a PCB supplier with the same word and different needs.
The first is an engineer who understands circuits but has never specified a board. The questions are concrete: how many layers, which material, how thick, what finish, what tolerance, and what will the fabricator do if the drawing is ambiguous. The risk is not misunderstanding the electronics; it is under-specifying the mechanical and process requirements, and finding out at first article.
The second is a buyer who has been handed a bill of materials and a deadline. The questions are equally concrete: what am I actually buying, which part of this specification drives the price, what information will stop the quotation being requoted, and how do I know whether two quotations describe the same board. The risk here is comparing prices for different products and concluding that one supplier is expensive.
This section is written for both, in that order, because the buyer's questions resolve faster once the engineer's vocabulary is in place.
The board, in the order you should think about it
A printed circuit board is a laminate structure that holds copper conductors so components can be mounted and connected without discrete wiring. That definition is stable. What varies is the construction, and construction is decided in a specific order.
Start with the electrical requirement: how many signal layers, whether there are controlled impedance traces, and whether any nets need plane references. That answer sets the layer count. Layer count then sets the stackup, which sets the material and prepreg combination, which sets the finished thickness. Thickness and stackup together set the drill aspect ratio, which constrains hole size. Hole size and line width together determine whether the design is comfortable or marginal at the chosen factory.
Working in that order produces a specification. Working backwards, from a finished thickness that someone wrote on a drawing, produces a stackup that may not be buildable.
The full sequence from data to finished board, including the controls at each step, is in the manufacturing process overview.
The four specifications that decide the price
Most of a bare-board price is determined by four decisions, all of which are made before a supplier is chosen.
Layer count is the largest single driver, because each pair of layers adds material and two lamination cycles. A six-layer design that could be four costs more in material, drilling and lamination simultaneously.
Minimum line width and spacing determines yield. Yield falls faster than feature size, which is why a design at the edge of a factory's capability is not simply a little more expensive; it can be disproportionately more expensive, and less reliable.
Hole size and count determines drilling time and plating difficulty. A small hole through a thick board is the hardest combination, and it is expressed as an aspect ratio. If the ratio exceeds what the factory routinely builds, the quotation acquires a caveat or a premium.
Surface finish determines both cost and solderability. HASL is inexpensive and forgiving; ENIG carries gold and nickel and is required for fine-pitch assembly and for certain storage and contact requirements. Specifying ENIG by habit is one of the most common avoidable costs on a drawing.
Everything else, including solder mask colour, legend and outline tolerance, is secondary to these four.
The vocabulary that changes a conversation
A short list, because a buyer who can use these words gets a different quality of answer.
A stackup is the ordered sequence of copper, prepreg and core with thicknesses. Prepreg is resin-impregnated glass that flows and bonds during lamination; the core is already cured. A via is a plated hole connecting layers, and it is buried, blind or through depending on which layers it reaches. The annular ring is the copper width around a drilled hole. The solder mask dam is the mask web between adjacent pads, and its width is a real design constraint rather than a cosmetic one.
Two more matter for buying rather than building. A panel is the production format the factory actually builds, containing one or more boards; the board price is the panel price divided by the boards on it. And finished hole size is not drilled hole size, because plating adds copper to the wall. Quoting one and specifying the other is a routine source of disagreement at first article.
The definition page in what is a PCB develops each of these with the physical layer they belong to.
Bare board and assembly are different products
The most expensive confusion in this section is between a board and an assembly. A bare board is fabricated from Gerber and drill data. An assembly is the board plus components plus solder, and it needs a BOM, placement data and assembly instructions in addition.
The prices are not comparable, the lead times are not comparable, and the acceptance criteria are different: bare-board electrical test checks connectivity within its defined scope, while assembly inspection and functional test address different questions entirely. A supplier who quotes both without separating the scopes has made a comparison impossible.
PCB versus PCBA sets out the file package for each, and bare-board testing explains what electrical test does and does not prove.
Where to go from here
If you are specifying a board, start with the material question, since FR-4 is a family rather than a single product: the materials index is the entry point. If you already have files and want to know whether they are complete, the fabrication file checklist is the faster route.
Either way, the useful habit is to write the specification down before asking for a price. A quotation against a written specification is a number you can compare. A quotation against a sentence is a starting position.
When you are ready, send the package and we will review it before quoting, including the parts of the drawing that a fabricator would otherwise resolve by assumption.