Engineer Reference · Bilingual EN/ZH

PCB DFM Design Guide

Design for Manufacturability determines prototype success and production yield. This guide covers six core design areas to help you avoid common fabrication issues before tape-out.

Trace Width & Spacing

线宽与线距

  • For standard FR-4, keep minimum trace width/spacing at 4 mil (0.1 mm); HDI processes can go below 3 mil
  • With 1 oz outer copper, plan roughly 1 A per mm of trace width for current; widen power traces or use copper pours
  • Insufficient spacing risks etching residues and shorts; keep at least 8 mil clearance in high-voltage areas

Drilling & Vias

钻孔与过孔

  • Keep mechanical drill holes at 0.2 mm (8 mil) minimum; laser micro-vias can reach 0.1 mm
  • Via pad diameter should exceed hole size by at least 0.25 mm to prevent pad lifting
  • Maintain 8 mil hole-to-trace clearance; use plugged or via-in-pad processes under BGA areas

Stackup Design

叠层设计

  • For 4-layer boards use Signal-GND-PWR-Signal stackup to give high-speed traces a solid reference plane
  • Use symmetric stackups for 6+ layers to prevent warpage, alternating core and prepreg
  • Place impedance-controlled layers adjacent to reference planes; keep dielectric tolerance within ±10%

Impedance Control

阻抗控制

  • Common targets: 50Ω single-ended, 90Ω differential (USB), 100Ω differential (Ethernet, HDMI)
  • Standard tolerance is ±10%; precision applications can request ±7% — specify it when ordering
  • Impedance depends on trace width, dielectric height and Dk; simulate with an impedance calculator before tape-out

Panelization & Tooling Edges

拼板与工艺边

  • Leave 5 mm tooling rails for SMT boards, or add them at panel level
  • V-scoring suits rectangular arrays; stamp holes suit irregular shapes — combine both when needed
  • Keep panel size within 400×400 mm and confirm compatibility with your assembly house equipment

Surface Finish Selection

表面处理选择

  • HASL is low-cost with good solderability but uneven surfaces — avoid for fine-pitch parts
  • ENIG offers flat surfaces and long shelf life, ideal for BGA and fine pitch at higher cost
  • OSP is cheap and flat but has short shelf life and limited reflow cycles — best for fast-turn orders

Soldermask & Silkscreen

阻焊与丝印

  • Keep soldermask dams at least 4 mil wide; for dense parts use mask-defined pads or drop local silkscreen
  • Silkscreen legends should be at least 1 mm high with 0.15 mm stroke to survive etching
  • Define mask coverage (tenting vs opening) explicitly in Gerber to avoid solder bridging

Gold Fingers & Edge Connectors

金手指与边缘连接器

  • Chamfer gold-finger edges at 45° or 30° for smooth insertion and plating protection
  • Avoid traces or vias under the finger area to prevent delamination from insertion stress
  • Standard gold thickness is 0.05 μm; use 0.76 μm hard gold for high-cycle connectors

Board Thickness & Tolerance

板厚与公差

  • Standard thickness is 1.6 mm with ±10% tolerance; aspect ratios above 10:1 sharply raise drilling and plating difficulty
  • Specify tolerance bands for routed slots and depth-controlled milling to avoid assembly interference
  • Keep warpage within 0.75% and confirm supplier measurement data before SMT

Test Points & Fiducials

测试点与基准点

  • Keep test points at least 0.9 mm in diameter on a 2.54 mm grid for bed-of-nails and flying-probe testing
  • Provide at least three global fiducials per side (diagonal plus one), plus local fiducials for fine-pitch parts
  • Keep a 5 mm keep-out around fiducials free of silkscreen and components for reliable recognition

Related Online Tools

DFM Online CheckImpedance CalculatorStackup Designer