The Journey from Raw Gold to Semiconductor-Grade Purity
Gold used in semiconductor chip wafer coating must meet extraordinary purity standards — far beyond what's required for jewelry or investment bars. While standard investment-grade gold is 99.99% pure (4N), semiconductor applications often demand 99.999% (5N) or even 99.9999% (6N) purity. A single impurity atom in the wrong place can cause a chip to fail.
This article examines the refining process that transforms raw gold into semiconductor-grade material suitable for chip wafer coating and electronic interconnections.
Stage 1: Primary Refining — The Miller Process
The Miller Process, named after Francis Bowyer Miller who developed it in 1867, is the primary industrial method for purifying gold:
**Chlorine gas is bubbled through molten impure gold** at approximately 1,100°C
**Impurity metals react with the chlorine** to form metal chlorides (which are lighter than gold and float to the surface as slag)
**Base metals** (copper, zinc, iron, lead) are removed first as they react most readily
**Silver** is then removed as silver chloride
**The result is gold of approximately 99.5-99.7% purity**
The Miller Process is fast and cost-effective for large-scale refining, making it the standard first-stage purification method at major refineries including our partner, IPMR (International Precious Metals Refiners).
Stage 2: Electrolytic Refining — The Wohlwill Process
To achieve the ultra-high purity required for semiconductor applications, Miller-processed gold undergoes electrolytic refining:
**Impure gold anodes** are dissolved in a hydrochloric acid/gold chloride electrolyte
**Pure gold deposits on the cathode** as impurities remain in solution or fall to the bottom as anode slime
**The result is gold of 99.99% (4N) purity or higher**
**Multiple passes** can achieve 99.999% (5N) purity
Stage 3: Zone Refining for Semiconductor Grade
For the highest purity levels required in semiconductor manufacturing:
**A narrow molten zone is passed along a gold rod** using induction heating
**Impurities preferentially segregate into the molten zone** and are swept to one end
**Multiple passes** progressively increase purity
**The result can exceed 99.9999% (6N) purity**
Quality Standards and Certification
LBMA Good Delivery Standard
The London Bullion Market Association (LBMA) Good Delivery standard is the global benchmark for gold bar quality:
Minimum fineness: 995.0 parts per thousand (99.5%)
Weight range: 350-430 troy ounces (approximately 10.9-13.4 kg)
Assay accuracy: Within ±0.5 parts per thousand
Physical appearance: Clean, free from surface cavities, properly stamped
Semiconductor-Specific Standards
Beyond LBMA, semiconductor-grade gold must meet additional specifications:
Purity: 99.99% minimum, often 99.999%+
Trace element limits: Individual impurity elements typically <1 ppm
Specific gravity: Within 0.1% of theoretical value
Surface quality: Free from oxides, organic contamination, and particulates
Our Refining Partnership with IPMR
Integrity Global Trade's partnership with IPMR (International Precious Metals Refiners) provides our clients access to:
State-of-the-art Miller Processing facility with capacity for industrial-scale refining
LBMA Good Delivery accreditation ensuring globally recognized quality standards
Multi-stage refining from doré to semiconductor-grade purity
Full assay certification with detailed impurity analysis for every batch
Chain-of-custody documentation from mine source through refining to final delivery
Every batch of refined gold comes with comprehensive quality documentation including assay certificates, material safety data sheets, and compliance records.
Why Source Semiconductor Gold Through Integrity Global Trade?
**Verified sourcing** — All gold originates from UN-certified, conflict-free mines
**Refinery quality** — IPMR partnership ensures LBMA-standard refining
**Full compliance** — KYC/AML verification on every transaction
**Traceability** — Complete chain-of-custody from mine to your facility
**Flexibility** — Available as wire, foil, pellets, sputtering targets, or custom forms
Contact Integrity Global Trade for semiconductor-grade gold and precious metals refined to the highest purity standards with full compliance documentation.