PCB / Inner layer image and etch

Bare board · 02

Inner layer image and etch

On multilayer boards the inner copper is printed and etched first. Two-layer ESP32 boards skip this step.

01 What happens

  • Dry film is laminated on the inner core, exposed to the inner artwork, developed, then etched.
  • AOI checks opens, shorts and remaining copper width before the cores go to press.
  • Registration holes and coupons are part of the inner panel, not optional artwork.

02 On an ESP32 board

  • A 4-layer ESP32 board often puts GND/power on inners. Thin dielectric helps impedance but is easier to wrinkle in press.
  • Return paths for USB and RF should be solid copper, not a patchwork of splits.
  • If you only need 2 layers, do not invent inner layers ‘for quality’ — extra lamination is extra warpage risk.

03 What usually fails

  • Under-etch (shorts) or over-etch (opens, thin traces that fail impedance).
  • Inner AOI skipped on a cheap quote — defects only show after drill and plate.
  • Wrong inner film: swapped L2/L3, mirrored pair.

04 What we check

  • We confirm layer count, inner copper weight and whether the quote includes inner AOI.
  • For RF or USB, we want a stack-up drawing the fab signed, not a generic ‘FR-4 1.6 mm’.

← Previous step: CAM and DFM incomingNext step: Lay-up and lamination →

中文

PCB工艺 / 内层图形与蚀刻

光板 · 02

内层图形与蚀刻

多层板先做内层曝光蚀刻。两层 ESP32 板没有这一步。

01 这一步做什么

  • 内层芯板贴干膜、曝光、显影、蚀刻。
  • 压合前 AOI 查开路、短路和残留线宽。
  • 定位孔和阻抗条是内层拼板的一部分，不是可有可无的图。

02 落到 ESP32 板上

  • 四层 ESP32 板内层常做地/电源。介质薄有利于阻抗，压合时也更容易起皱。
  • USB、射频回流路径要整片铜，不要切得稀碎。
  • 两层就够时不要为了「看起来高级」加内层——多一次压合就多一份翘曲。

03 常见失败

  • 蚀刻不足短路，蚀刻过猛开路或线变细、阻抗跑掉。
  • 便宜报价不做内层 AOI，钻孔电镀后才暴露。
  • 内层菲林反了、L2/L3 对调。

04 我们查什么

  • 核对层数、内层铜厚、报价里有没有内层 AOI。
  • 射频或 USB 要工厂签过的叠层，不要一句「FR-4 1.6 mm」打发。

← 上一步: CAM 与 DFM 来料下一步: 叠层与压合 →