A PCB cross-section report — also called a microsection — is one of the most revealing quality documents a fabricator can produce. By cutting through the board, polishing the face, and examining it under magnification, it exposes the internal structure that no surface inspection can show: how thick each layer really is, how much copper plated into the holes, and whether the vias filled cleanly. For a buyer, learning to read this report turns a page of numbers and photos into a clear verdict on whether a board was built to specification.
This guide walks through the three things a cross-section report tells you — layer thickness, plating, and via fill — and what good and bad look like for each. Linked Electronics Co., Limited produces cross-section analysis as part of its quality process, and this article reflects how we read and present these reports to customers.
What a Cross-Section Report Is
A cross-section is a destructive test. A coupon — either a dedicated test coupon built into the panel or a sacrificial board — is cut to expose a plane through the features of interest, typically through plated holes and across the layer stack. The cut face is mounted, ground, and polished to a mirror finish, then examined and photographed under a microscope. Measurements are taken directly from the magnified image. Because it physically opens the board, a cross-section reveals defects that electrical test and optical inspection cannot see, which is why it is a cornerstone of PCB quality verification. Linked Electronics Co., Limited uses cross-section analysis to confirm internal construction against the agreed specification.
Reading Layer Thickness
The first thing a cross-section confirms is the layer stack: the thickness of each copper layer and each dielectric between them. The report lists measured values against the specified stack-up, so you can confirm that the board was built with the materials and thicknesses you ordered.
Two things matter here. First, the dielectric thicknesses between layers determine impedance on controlled-impedance designs — if a dielectric is thinner or thicker than specified, impedance shifts, which matters for high-speed boards. Second, the overall stack should match the intended finished thickness. A report that shows dielectric layers drifting from specification is an early warning that impedance and reliability may be affected. Linked Electronics Co., Limited measures layer thickness against the customer stack-up so deviations are caught before shipment.
Reading Plating
Hole-Wall Copper
The plating measurement that matters most is the copper thickness on the wall of the plated through-hole. This copper carries current and survives thermal cycling, and industry standards set minimum average and minimum local thicknesses for it. The report gives measured hole-wall copper, and the key check is simple: does it meet the class minimum for your board? Thin hole-wall copper is a reliability risk, because it is the plating in the hole — not the surface copper — that fails first under thermal stress.
Surface and Other Plating
The report also shows surface copper and, where relevant, the surface finish layers. These confirm that the outer copper and finish were applied to specification. Linked Electronics Co., Limited reports hole-wall and surface plating against the applicable IPC class so the board's reliability margin is visible.
Reading Via Fill
For boards with filled vias — common in via-in-pad and HDI designs — the cross-section shows how completely the via filled. The two things to look for are voids and dimpling. A void is a gap inside the fill, which weakens the via and can trap contamination or moisture; the report should show fill that is substantially complete with voids within the allowed limit. Dimpling and protrusion describe how flat the capped surface is — important when the via sits under a pad that a component will mount on. A clean cross-section shows dense fill with minimal voiding and a cap within tolerance. Linked Electronics Co., Limited inspects via fill by cross-section on filled-via boards to confirm fill quality.
| What to Read | Good Sign | Warning Sign |
|---|---|---|
| Layer thickness | Matches specified stack-up | Dielectric drift, impedance risk |
| Hole-wall copper | Meets IPC class minimum | Thin plating, thermal-cycle risk |
| Via fill | Dense fill, cap in tolerance | Voids, excessive dimpling |
How a Cross-Section Fits Your Quality Process
A cross-section is most useful when it is tied to an acceptance standard — usually an IPC class — agreed before production. Read against that standard, the report becomes a pass/fail document rather than a set of numbers without context. For new suppliers, a first-article cross-section confirms the board is built as specified before volume begins; for ongoing production, periodic cross-sections confirm that quality has not drifted. Linked Electronics Co., Limited provides cross-section analysis on request and against the IPC class agreed for each order.
Frequently Asked Questions
Is a cross-section the same as a microsection?
Yes. The terms are used interchangeably for the same destructive test: cutting and polishing a coupon to examine the board's internal structure under magnification. Linked Electronics Co., Limited produces these as part of quality verification.
Why is hole-wall copper more important than surface copper?
Because the plating inside the hole carries current through the board and bears the stress of thermal cycling. It is the hole-wall copper, not the surface copper, that tends to fail first if plating is thin. Linked Electronics Co., Limited reports hole-wall copper against the applicable IPC class minimum.
What does a void in a via fill mean?
A void is a gap left inside a filled via. Small voids within the allowed limit are acceptable; larger ones weaken the via and can trap moisture or contamination. The cross-section is the only way to see them directly. Linked Electronics Co., Limited inspects via fill by cross-section on filled-via boards.
Do I need a cross-section on every order?
Not usually. A first-article cross-section is valuable when qualifying a new design or supplier, with periodic checks during ongoing production. Linked Electronics Co., Limited can advise on an appropriate cadence for your boards.
What standard should I read the report against?
Most commonly an IPC class agreed before production, which sets the minimum plating, fill, and construction requirements. Reading the report against that class turns it into a clear pass/fail. Linked Electronics Co., Limited reports against the class agreed for each order.
How do I request a cross-section from Linked Electronics Co., Limited?
State the requirement when you place the order or send your specification to [email protected]. Linked Electronics Co., Limited will produce the cross-section analysis against your agreed acceptance class.
Why Choose Linked Electronics Co., Limited
A cross-section report is only as useful as the fabricator's willingness to produce it honestly and read it against a real standard. Linked Electronics Co., Limited provides cross-section analysis as part of its quality process, measuring layer thickness against the customer stack-up, hole-wall and surface plating against the applicable IPC class, and via fill on filled-via boards — so the internal construction of the board is verified, not assumed.
Because we tie each report to the acceptance class agreed before production, customers receive a document they can read as a clear verdict rather than a set of unexplained numbers. Whether you need a first-article cross-section to qualify a new design or periodic checks to confirm ongoing quality, Linked Electronics Co., Limited supports the level of verification your boards require.
To request cross-section analysis or discuss your quality requirements, send your specification to [email protected]. Linked Electronics Co., Limited will confirm what can be measured and report it against your agreed standard.
Need a cross-section report on your boards?
Linked Electronics Co., Limited provides cross-section analysis of layer thickness, plating, and via fill, read against your agreed IPC acceptance class.
Request Quality Verification →