Last updated: 2026-09-05 · 5 min read

Micro Injection Molding — What Are the Feature Limits, Mold Requirements and Process Controls for Sub-Millimeter Parts?

Micro injection molding produces parts with features as small as 50–100 μm, part weights under 1 gram and wall thicknesses of 0.05–0.5mm. The process requires specialized machines with 5–15mm screws (shot repeatability ±0.5% vs. ±2–5% for standard machines), mold cavities machined by micro-EDM or LIGA, and cavity pressure monitoring at 1,000+ Hz sampling rates. Standard machines cannot fill micro-features reliably — the melt freezes before the cavity is full.

Key Facts

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  • Feature size limits: minimum wall 0.05mm (50 μm), minimum hole diameter 0.1mm (100 μm), minimum rib width 0.08mm. These limits depend on the resin’s MFI and the mold’s machining capability. LCP and high-MFI PC fill the smallest features; glass-filled resins cannot because fibers (3–5mm long) block micro-channels below 0.2mm.
  • Mold machining: micro cavities are machined by micro-EDM with electrode diameters of 0.05–0.3mm, or by LIGA (X-ray lithography + electroforming) for features below 50 μm. CNC machining reaches approximately 0.1mm feature size — below that, EDM or LIGA is required.
  • Process control: micro molding requires cavity pressure monitoring at 1,000–10,000 Hz sampling rate to detect fill variations of ±0.1 MPa. Standard pressure sensors at 100 Hz cannot detect the micro-second variations that cause short shots or flash in micro-cavities.

    • Cavity — The hollow space inside the mold that forms the part shape. Multi-cavity molds produce multiple parts per shot. Cavity count determines production output but also mold cost and complexity. Each cavity must be balanced for uniform fill. The related guide covers adjacent topics.

    How Do Micro Molding and Standard Molding Compare Across Five Key Parameters?

    Factor Micro Molding Standard Molding
    Part weight 0.001–1 gram 1–500 grams
    Min wall thickness 0.05mm (50 μm) 0.5mm (500 μm)
    Min feature size 50–100 μm 0.5–1.0mm
    Screw diameter 5–15mm 20–100mm
    Shot repeatability ±0.5% ±2–5%

    The 10× difference in shot repeatability (±0.5% vs. ±2–5%) is what makes micro molding possible at all. A standard machine’s ±3% variation on a 0.01 gram shot means the actual shot weight varies from 0.0097 to 0.0103 grams — a 6% range that is enough to cause short shots in half the parts. A micro machine’s ±0.5% on the same shot gives a 1% range — tight enough for consistent fill.

    What Three Design Rules Govern Micro-Molded Parts?

    1. Resin selection: LCP fills the smallest features. Liquid crystal polymer (LCP) has extremely high MFI and molecular orientation along the flow direction — it fills features down to 50 μm. High-MFI PC (MFI 30–60 g/10min) is used for transparent micro-parts.
      Glass-filled resins are not suitable because fibers (typically 3–5mm long) cannot flow through channels smaller than 0.2mm — the fibers jam at the channel entrance and block fill.
    2. Gate design: pin-point gates of 0.1–0.3mm diameter. The gate must freeze quickly to prevent drooling but open fully during injection. Valve gates are not practical at this scale because the valve pin mass creates inertia that prevents micro-second response.
      The gate location must be optimized so the melt fills all micro-features before freezing — gate placement errors are not correctable by process tuning.
    3. Venting: vent depths of 0.005–0.01mm (5–10 μm). Deeper vents allow flash in the micro-features. The vent land length must be less than 1mm to prevent the melt from freezing in the vent before the air is evacuated.
      Micro cavities trap air more easily than standard cavities because the flow front velocity is higher and the air has less time to escape through the vent channels.

    Shrinkage — The dimensional reduction from mold cavity to cooled part. Amorphous resins: 0.4–0.7% (uniform). Semi-crystalline: 1.0–2.5% (directional).
    Mold makers apply shrinkage factor when machining cavity. Actual shrinkage varies with wall thickness, gate location and packing pressure. The related guide covers adjacent topics.

    Micro molding: features 50–100 μm, walls 0.05–0.5mm, weight under 1g. Machine: 5–15mm screw, ±0.5% repeatability. Mold: micro-EDM (0.05–0.3mm electrodes) or LIGA for features below 50 μm. Gate: 0.1–0.3mm pin-point. Vent: 5–10 μm depth. Process monitoring: 1,000–10,000 Hz cavity pressure. Single-cavity micro mold: $20,000–80,000.

  • Key parameter identified — critical variable confirmed against spec.
  • Tolerance within achievable range — commercial ±0.15mm or tighter as needed.
  • Material matched to application — resin grade selected for end-use environment.
  • Process window validated at T1 — parameters locked after first trial.
  • Inspection method defined — CMM, visual, or functional test specified.

    • Frequently Asked Questions

    What tolerances are achievable in micro molding?

    Micro molding holds tolerances of ±0.005mm (5 μm) on critical dimensions — limited by mold machining accuracy, resin shrinkage variation and process repeatability. For features below 0.1mm, the tolerance is typically ±10% of the feature size.

    The mold maker should provide a capability study (Cpk data) for the critical micro-features. A Cpk below 1.33 indicates the process is not stable enough for production — the mold or process parameters need adjustment before the mold is approved.

    Can micro molding be done on standard injection machines?

    No — standard machines have shot sizes of 5–500 grams and cannot control the 0.001–1 gram shots required for micro molding. The injection speed, pressure and position control on a standard machine are not precise enough for micro-cavities.

    A dedicated micro-molding machine with a 5–15mm screw and high-resolution feedback is required. The machine’s closed-loop control adjusts injection speed and pressure in real time at micro-second intervals — something a standard machine’s hydraulic system cannot achieve.

    How do you inspect micro-molded parts?

    Micro-molded parts are inspected by optical microscopy (50–500× magnification) for surface features, SEM (scanning electron microscopy) for sub-micron details, and optical comparators for dimensional measurement. CMMs with 1 μm resolution can measure features down to 0.1mm.

    The inspection method must match the feature size — a standard CMM with 3 μm resolution cannot reliably measure a 50 μm feature. For production inspection, automated optical inspection (AOI) systems with 1–5 μm resolution are used to check every part at line speed.

    Key Takeaways

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  • Micro molding: features 50–100 μm, walls 0.05–0.5mm, weight under 1g, ±0.5% repeatability.
  • LCP fills smallest features; glass-filled resins cannot. Gate 0.1–0.3mm, vent 5–10 μm.
  • Mold: micro-EDM or LIGA. Process monitoring: 1,000–10,000 Hz cavity pressure.
  • Single-cavity micro mold: $20,000–80,000. Tolerance: ±5 μm on critical dims.

    • Send the micro-part drawing with feature sizes and tolerance requirements — the quotation evaluates the mold machining method, resin selection and inspection plan so the micro-molding feasibility is confirmed before the tool is ordered.

    Sources: Plastics Technology — Micro Injection Molding Process and Equipment · Society of Plastics Engineers (SPE) — Micro-Molding Design Guidelines and Capability Data · MoldMaking Technology — Micro Mold Machining and Inspection Methods · Bamberg Engineering — Micro Molding Design Rules and Material Selection · ASTM International — Micro-Molding Dimensional Test Standards

    — Arthur, Tooling Engineer at aCatMould