A common RFQ loop looks like this. The customer reads the capability table, sees minimum trace/space of 2mil/2mil, minimum hole size of 0.075mm and an aspect ratio of 10:1, designs to those numbers, and gets back "engineering review required" or "please relax this dimension." The natural response is: your table says you can do this.
Both sides are right. The misunderstanding sits in how capability tables are read: every row states what that one parameter can reach on its own. Nothing in the table promises that two rows hold simultaneously.
That is not a hedge. Manufacturing capability is a set of process windows that compete for the same margin. Stack several limits onto one board and the windows eat each other. This article covers three things: which parameters conflict by nature, what the same number means across three tiers of commitment, and which missing design inputs force a fabricator to answer at the most conservative tier.
For how thickness tolerance itself is specified, see finished thickness tolerance control. For stackup construction, see the multilayer stackup guide. This article is only about how the parameters interact.
1. Three ways capability tables get misread
Our PCB manufacturing capabilities page lists parameters in four groups: basic parameters, drilling capability, surface finish and special processes. The groups sit side by side. They are not a configurator.
Misread one: treating a limit as a default. The 0.075mm minimum hole size is what laser drilling reaches under suitable buildup conditions. It does not mean every hole can be drawn at 0.075mm. Mechanical drilling bottoms out at 0.15mm. Two different processes, two different windows. A board full of 0.075mm holes means everything goes laser, which changes the process route and the stackup.
Misread two: reading single limits as a combination. The copper weight ceiling of >12oz is real. So is 2mil/2mil minimum trace/space. They cannot apply to the same layer. Section 2 explains why.
Misread three: treating a checkmark as unconditional. Resin plugging, copper paste fill, castellated holes and gold fingers all carry ✓ under special processes. That confirms the process exists in-house. It does not confirm it works at your hole size, board thickness and stackup. A ✓ answers "do you have this step," not "can I use it this way."
2. Three pairs that conflict by nature
2.1 Copper weight × trace/space
This is the least negotiable pair. Etching works down from the copper surface. Thicker copper needs longer etch time, and more copper is removed sideways along the way. The conductor cross-section shifts from rectangular toward trapezoidal: trace width narrows, spacing widens.
So 2mil/2mil belongs to thin copper layers. As copper moves toward 3oz, 6oz and 12oz, the achievable minimum trace/space scales up with it. The 0.5oz to >12oz range on the capability page spans several distinct product classes. It is not a slider you move freely within one board. Heavy copper trace rules and compensation logic are covered in heavy copper weight tiers.
Order of decisions: fix copper weight first (driven by current carrying and heat spreading), then ask what minimum trace/space that copper weight allows. Locking trace width first and discussing copper later usually means a redesign.
2.2 Board thickness × minimum hole size × aspect ratio
One constraint binds these three: aspect ratio = board thickness ÷ hole diameter, capped at 10:1 max on our capability page.
Practically, you get to choose two of the three freely. The third is computed and has to land inside the cap. Take board thickness at the 6.0mm ceiling: at 10:1, hole diameter cannot go below roughly 0.6mm. That is nearly an order of magnitude away from the 0.075mm minimum hole size listed elsewhere in the same table. Neither number is wrong. They simply never hold on the same board.
Aspect ratio is a hard constraint because it governs whether plating solution can exchange evenly inside the barrel. The deeper and narrower the hole, the harder it is for the mid-barrel deposit to keep up with the entry. Barrel quality acceptance is covered in drilling hole quality inspection. HDI solves this by having laser vias span a single dielectric layer, pulling aspect ratio down at the source rather than forcing it on through-holes. That route's design inputs are in HDI buildup and copper plating thickness inputs.
2.3 Impedance tolerance × stackup freedom
Our capability page states impedance control as ±5% (±10% standard). It reads like a test-stage capability. It is actually margin left over jointly by stackup design and the etch window.
Impedance is set by trace width, copper weight, dielectric thickness and dielectric constant. Once a fabricator has the drawing, the usual adjustable levers are trace width (trimmed inside an allowed range) and dielectric thickness (selected from available material thicknesses). Lock trace width, dielectric thickness and layer count all at once while demanding ±5%, and there is no lever left. The honest answers become "review required" or acceptance at ±10%.
The workable way to specify it: give target impedance and tolerance, mark which parameters are functional and fixed, and leave stackup configuration to the fabricator. Tolerance class selection is covered in impedance control tolerance classes.
3. Standard, available, review required: one number, three certainties
A capability table has one value column. Internally, every parameter carries at least three tiers. Knowing them removes a lot of back-and-forth.
Standard. Delivered stably on the normal process route, normal materials and normal capacity. No extra review, quoting and lead time follow the standard path. This tier covers the large majority of requirements.
Available. Process-feasible, but needs a specified route: laser drilling instead of mechanical, a particular buildup, an added step. Most of the headline limits on a capability table live here, and cost or schedule may shift.
Engineering review required. No parameter exceeds its ceiling, but the combination presses against several window edges at once, so engineering has to make a DFM call first. Review required is not a refusal. It means nobody can responsibly answer yes or no before seeing the complete design input.
A quick heuristic: count how many limits your design touches. One is usually "available." Two or more, expect review. Under quick-turn conditions these tiers compress further; the boundaries are in quick-turn process window limits.
4. Missing inputs shrink the answer
Fabricators answer based on the information supplied. When information is incomplete, the only defensible answer assumes the most conservative case. These fields decide which tier of answer you get:
| Design input | Consequence if missing |
|---|---|
| Layer count and stackup requirement (or "fabricator to configure") | Aspect ratio and impedance feasibility cannot be assessed; answer defaults to standard |
| Copper weight per layer, inner and outer distinguished | Trace/space feasibility cannot be checked |
| Finished thickness and tolerance | Aspect ratio cannot be computed |
| Minimum hole list grouped by hole type, mechanical vs laser | Drilling route cannot be fixed |
| Impedance: target, tolerance, and which parameters may be adjusted | Only the ±10% standard tier can be committed |
| Surface finish and special processes (plug type, castellation, gold fingers) | Step order and mutual effects cannot be verified |
| Acceptance class and inspection basis | Reject criteria remain undefined |
The most frequently omitted item is the last part of the impedance row: which parameters may be adjusted. Engineering-wise, naming your adjustable items explicitly gets you tighter tolerance more often than locking everything down. Full tolerance definitions are on the tolerance page; pre-release self-checks are in the stackup drawing release checklist.
5. A three-step check
Applied to any supplier's capability table, this order works better than comparing values row by row.
Step one: mark the limits you touch. Compare your parameters against the table and circle anything at or near a ceiling. Zero limits touched: standard flow. One: note it and ask which tier that item sits in. Two or more: request DFM review directly rather than waiting for the quote to come back and then redesigning.
Step two: check the three conflicts. Does copper weight match the trace/space you drew? Is board thickness ÷ minimum hole diameter inside 10:1? Does the impedance requirement leave the fabricator an adjustable parameter? These three self-checks catch most rework.
Step three: write the adjustable items into the file. State in the drawing or notes which dimensions are functional and fixed, and which the fabricator may optimise within a range. This step decides whether you receive "review required" or a concrete plan.
To get a call on a specific combination, submit the stackup requirement together with the hole list through quote and engineering review; engineering responds against the order above.
FAQ
Q: The table says 2mil/2mil. Why can't my board have it?
A: 2mil/2mil belongs to thin copper layers. If your board uses heavier copper, sideways etch consumes the trace and space margin and the achievable minimum scales up. Confirm copper weight per layer first, then ask for the trace/space floor at that weight.
Q: Can 6.0mm board thickness and 0.075mm minimum hole size be used together?
A: No. The aspect ratio cap is 10:1, so a 6.0mm board puts the hole floor at roughly 0.6mm. Those two values are separate single-parameter limits and do not form a combination.
Q: Does "engineering review required" mean it cannot be done?
A: No. It means the combination presses against several process windows, so engineering needs the complete design input before committing. Supplying full stackup, copper weights, hole list and impedance requirements usually converts a review into a definite plan.
Q: For ±5% impedance, should I lock trace width and dielectric thickness in the drawing?
A: Not recommended. Impedance depends on trace width, copper weight, dielectric thickness and dielectric constant together. Locking all of them removes the fabricator's adjustment freedom, which pushes the commitment back to ±10%. Give target and tolerance, and name the adjustable items.
Q: What does the ✓ in the special processes column mean?
A: It confirms the process is available in-house. It does not mean it is unconditionally usable on your board. Plug type, castellation and gold fingers still have to be checked against your hole size, board thickness and stackup.
Q: How do I tell quickly whether to request DFM up front?
A: Count the limits your design touches. Zero means standard flow, one means note it and ask the tier, two or more means request review directly.