How Dimer Purity of Parylene Affects Coating Quality

Linking ppm-level impurities to film performance, yield and reliability

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Dimer purity of Parylene is a primary driver of coating quality. Trace non-volatile residues (NVR), moisture, particulates and side products can seed pinholes, haze and rate instabilityβ€”ultimately reducing dielectric strength and long-term reliability. This guide explains how purity translates into visible and latent defects, what to include on your acceptance criteria & COA, and how handling and storage protect quality.

Further reading: Wikipedia – Parylene

How Dimer Purity Affects Parylene Coating Quality – Infographic showing how high-purity dimers produce cleaner deposition, smoother films and stronger adhesion.

Overview

Even with identical deposition hardware, dimer purity of Parylene will shift base pressure, rate stability and film morphology. Four impurity classes matter most:

  • NVR/ash – non-sublimable residues that foul crucibles and increase haze/roughness.
  • Particulates – seed nodules and pinholes; often introduced during transfer/loading.
  • Moisture – raises bubble/foam risk and contributes to local thin spots.
  • Side products/solvent traces – can depress dielectric strength and elevate leakage.

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Purity Metrics & COA Essentials

Your supplier’s Certificate of Analysis should include the followingβ€”align these with your internal spec:

Metric What It Shows Typical Target
Purity (GC/HPLC) Main dimer content vs side products β‰₯99.8% electronics; β‰₯99.9% critical builds
NVR/Ash (TGA) Non-sublimable residue at process temp ≀0.10% (tighten for high-rel)
Moisture (Karl Fischer) Water content driving bubbles/foam Low ppm, with alarm threshold set
Particle Cleanliness Counts of >10 ΞΌm contaminants Supplier statement + incoming spot checks
Identity (DSC/Melt) Confirms dimer type; flags contamination Matches reference range per grade
Traceability Batch ID, pack date, packaging type Mandatory on all lots

Set your own release, warn and reject bands and align them with product risk classification (e.g., aerospace, medical, safety-critical).

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Impurity β†’ Process β†’ Defect

The following summary links impurity classes to process symptoms and the defects you’ll see at inspection when the dimer purity of Parylene is poor:

Impurity Process Effect Typical Defects Risk
NVR/Ash Crucible fouling, rate drift Haze, roughness, orange peel High
Particulates Contaminated monomer flow Nodules, inclusions, pinholes High
Moisture Bubble formation, thin spots Bubbles/foam, microvoids Medium-High
Side products/solvent Electrical property drift Higher leakage, lower breakdown Medium

Tip: Place witness coupons in shadowed regions to reveal particulate and dewetting tendencies that normal boards may hide.

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Acceptance Criteria & Tests

Define clear release thresholds for the dimer purity of Parylene and verify at incoming inspection. Suggested bands:

  • Purity: β‰₯99.8% (electronics); β‰₯99.9% (safety-critical/medical).
  • NVR/Ash: ≀0.10% typical; tighten where dielectric margin is low.
  • Moisture: Low ppm; quarantine above alarm limit.
  • Particles: Supplier declaration plus membrane patch spot checks.
Verification Test Purpose Notes
TGA (Residue) Confirms non-volatile content Proxy for haze/orange-peel risk
GC-MS/HPLC Profiles side products Tracks lot-to-lot variation
KF Moisture Detects water uptake Correlates with bubbles/foam
DSC/Melt Identity confirmation Flags contamination or mix-ups
Witness Film + SIR Functional validation Dielectric & leakage performance

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Handling & Storage

Consistent handling protects purity between COA and deposition:

  • Dry & clean transfer: Sieve in a clean hood; use dedicated tools per dimer grade.
  • Moisture control: Keep sealed with desiccant; minimise ambient exposure during loads.
  • Crucible housekeeping: Remove legacy residue; pre-bake new crucibles.
  • Process trending: Track base pressure and rate; investigate drift immediately.
  • FIFO & re-test: Rotate stock; re-check moisture on aged lots.

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Why Choose SCH Services?

Partner with SCH Services for a complete, integrated platform: Conformal Coating, Parylene & ProShieldESD Solutions plus equipment, materials, and training. Our team brings decades of hands-on expertise.

  • ✈️ 25+ Years of Expertise – Trusted across aerospace, medical, defence, automotive, and electronics.
  • πŸ› οΈ End-to-End Support – From purity specs and incoming QA to deposition parameters and inspection.
  • πŸ“ˆ Scalable Capacity – From prototypes to high-volume production.
  • 🌍 Global Reach – Responsive support across Europe, North America, and Asia.
  • βœ… Proven Reliability – Consistent quality and strong customer satisfaction.

πŸ“ž Call: +44 (0)1226 249019 βœ‰ Email: sales@schservices.com πŸ’¬ Contact Us β€Ί

Note: This article provides general technical guidance only. Final design, safety, and compliance decisions must be verified by the product manufacturer and validated against the applicable standards.