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PCB Meaning Explained: 12 Terms Buyers and Engineers Use Differently
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# PCB Meaning Explained: 12 Terms Buyers and Engineers Use Differently
Twelve PCB terms that mean different things to the designer and the buyer, and the ones where the gap changes the price or the acceptance decision rather than just the conversation.
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## The short answer
Most disagreements on a PCB order are not about capability. They are about two people using the same word for different things, and neither noticing until the boards arrive.
A designer says "0.3 mm hole" and means the drill. A buyer reads the quotation, sees 0.3 mm, and expects a 0.3 mm hole in the finished board. Both are right in their own vocabulary, and the finished hole is 0.25 mm. Nothing was misquoted and nobody lied; the two parties were describing different objects with one number.
Twelve terms carry that risk. Three of them cost real money.
## The twelve, and where the gap sits
Read the last column as the filter. Where it says no, the gap costs a conversation. Where it says yes, the gap costs a re-quote, a re-spin or a rejected lot.
| Term | Designer means | Buyer hears | Changes price? |
| --- | --- | --- | --- |
| PCB | Bare board, no parts | Finished product | Yes |
| PWB | Older name, same object | A different product | No |
| Pad | Copper you solder to | A hole | Yes |
| Via | Plated hole between layers | Any small hole | Yes |
| Annular ring | Copper width around the hole | Pad diameter | Yes |
| Drill size | Tool diameter | Finished hole | Yes |
| Copper weight | Ounces per square foot | Thickness in mm | Yes |
| Solder mask | Permanent board coating | Solder paste | No |
| Silkscreen | Printed legend | Any printed layer | Sometimes |
| Tg | Softening point, reversible | Max operating temperature | Yes |
| Td | Decomposition point | Same as Tg | Yes |
| Panel | The manufacturing panel | One board | Yes |
## The three that cost the most
### Finished hole versus drill size
Every plated hole gets copper in it. A 0.30 mm drill becomes roughly a 0.25 mm finished hole after plating, and the exact reduction depends on the plating thickness the class requires. If your component lead needs 0.28 mm of clearance, a 0.30 mm drill does not give it.
Write both numbers on the fabrication drawing: drill size and finished hole size. A fabricator who receives only one of them will assume the other, and the assumption that protects their process is not always the one that protects your assembly.
### Copper weight versus copper thickness
Copper is specified in ounces per square foot, a unit from an era when foil was sold by weight. One ounce is about 35 µm. The conversion is not linear in practice above 2 oz because plating adds to the base foil, so a "2 oz" board may have 70 µm of copper on an outer layer, part foil and part plating.
If a design needs 100 µm of copper for current-carrying capacity, specify the requirement, not the ounce figure, and let the fabricator confirm the build. The difference between 2 oz and 3 oz is a step change in etch capability and in price.
### Tg versus Td
Tg is the temperature where the resin softens. It is reversible — cool the board and the property returns. Td is where the resin chemically decomposes. It is not reversible, and it is a different number.
A high-Tg laminate is not automatically a high-Td laminate, and the failure people worry about at reflow is closer to the second than the first. This is the subject of
[the FR-4 versus high-Tg comparison ↗](https://www.chinasuqi.com/en/blog/fr-4-vs-high-tg-laminate-when-the-upgrade-pays/)
, and it is the single most common place where a specification sounds rigorous and is not.
## Two terms people use to mean the opposite
"Pad" and "hole" get swapped constantly in assembly drawings, which matters because a pad with a hole in the wrong place is a drill error rather than a routing error, and drill errors are caught later.
"Solder mask" and "solder paste" get swapped in conversations with contract manufacturers, which is worse, because one is a permanent board coating and the other is a temporary printing step. A drawing that annotates "mask" over a component pad has stated the opposite of what the designer wanted.
## A purchase order line, read twice
Here is a line that appears, in some form, on a large share of orders:
"4-layer FR-4, 1.6 mm, 1 oz, HASL, 0.3 mm holes, 100 pcs."
Read by a designer, that is a complete instruction. Read by a fabricator, it is six questions. One ounce on which layers — all four, or outer only? Holes 0.3 mm drill or finished? Minimum annular ring implied by 0.3 mm holes on a 0.6 mm pad, or pads sized to the ring? HASL leaded or lead-free? "100 pcs" boards or panels? And 1.6 mm finished thickness, or nominal laminate thickness that finishes at 1.55 mm after plating?
None of those questions is pedantic. Each one has two plausible answers with a different price, and the factory will choose the answer that protects its process if nobody chooses for it. Six small decisions, made by someone who has never seen the product.
The fix is not a longer purchase order. It is a stackup drawing that states layer-by-layer copper, a drill table that states finished sizes, a note that names the finish exactly, and a quantity line that says boards and panels separately. Four documents instead of one sentence, and the questions disappear.
If a term appears in both your drawing and your purchase order and the two documents do not say the same thing, the factory will follow the drawing, because the drawing is what the machine reads.
## A one-page check before you send the file
None of these take long to write and all of them remove a round of questions.
Holes: drill size and finished size both stated, or a note that the drawing uses finished size throughout
Copper: weight stated with the layers it applies to, not implied for the whole board
Laminate: Tg and Td stated separately, with the grade name and the manufacturer if it is qualified
Mask: opening relative to pad stated as a rule, not as a single dimension
Quantity: boards and panels distinguished, with the panelisation drawing attached
## What we can and cannot do
We will read your drawing in the vocabulary it uses and ask when a number is ambiguous, which is the useful part of a DFM review — the checks in
[the Gerber review list ↗](https://www.chinasuqi.com/en/blog/gerber-dfm-check-twelve-errors-that-stop-a-file/)
exist because most ambiguity becomes visible only when the files are opened.
What we cannot do is guess which of two meanings you intended. If the drawing says 0.3 mm and the assembly needs 0.28 mm of clearance, only you know which constraint is real. For the wider vocabulary,
[the working definition of a PCB ↗](https://www.chinasuqi.com/en/blog/what-is-a-pcb-a-working-definition-for-engineers-and-buyers/)
covers the object itself, and the file package that removes most of these ambiguities is listed in
[the file checklist ↗](https://www.chinasuqi.com/en/resources/file-preparation/)
.
CONTINUE YOUR REVIEW
## Related manufacturing resources
Explore
### [PCB Basics ↗](https://www.chinasuqi.com/en/blog/pcb-basics/)
A starting point for engineers and buyers new to printed circuit boards: what the board is made of, how it is built, which terms matter and which specifications a quotation depends on.
guide
### [What Is a PCB? A Working Definition for Engineers and Buyers ↗](https://www.chinasuqi.com/en/blog/what-is-a-pcb-a-working-definition-for-engineers-and-buyers/)
A PCB is a laminated structure that carries copper conductors and connects components. A definition built around the five layers, six process steps and four specifications a quotation needs.
guide
### [PCB Layer Stackup Design: Reference Builds for 4, 6 and 8 Layers ↗](https://www.chinasuqi.com/en/blog/pcb-layer-stackup-design-reference-builds-for-4-6-and-8-layers/)
Four working stackups you can hand to a fabricator, what each one costs, and the three constraints that override any drawing: impedance target, finished thickness and copper weight.
guide
### [Gerber DFM Check: Twelve Errors That Stop a File at Review ↗](https://www.chinasuqi.com/en/blog/gerber-dfm-check-twelve-errors-that-stop-a-file/)
Twelve defects that show up in a Gerber package before fabrication starts, what each one costs if it survives to the drill, and which of them only the designer can fix.
YOUR NEXT PCB PROJECT
## Let’s define your next build.
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[Prepare a PCB inquiry ↗](https://www.chinasuqi.com/en/request-a-quote/)

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