| HS Code | 585469 |
| Product Name | Acidic Etchant Electronic/EL Grade |
| Grade | Electronic/EL Grade |
| Chemical Nature | Aqueous acidic solution containing inorganic acids |
| Physical State | Liquid |
| Appearance | Clear, colorless liquid |
| Odor | Pungent, irritating acidic odor |
| Ph | < 1 |
| Acidity | Strongly acidic |
| Specific Gravity | Approximately 1.0 - 1.3 at 20°C |
| Density | Approximately 1.0 - 1.3 g/mL at 20°C |
| Boiling Point | Above 100°C (aqueous acidic solution) |
| Freezing Point | At or below 0°C (depends on acid concentration) |
| Solubility | Completely miscible with water |
| Vapor Pressure | Comparable to water; approximately 2.3 kPa at 20°C |
| Flash Point | None (non-flammable aqueous solution) |
| Corrosivity | Corrosive to most metals, skin, and eyes |
| Purity | High purity with controlled trace metal impurities |
| Concentration | Mixed acid concentration typical for electronic-grade etching |
As an accredited Acidic Etchant Electronic/EL Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaged in a 4-liter high-purity HDPE bottle with leak-proof cap, labeled for safety, ensuring ultra-clean Electronic/EL Grade acidic etchant delivery. |
| Container Loading (20′ FCL) | 20′ FCL container for Acidic Etchant Electronic/EL Grade: corrosive, hazardous liquid. Ensure proper packaging, labeling, and UN-certified drums for safe transport. |
| Shipping | This corrosive, high-purity etchant requires hazardous material shipping. Pack in sealed, corrosion-resistant containers, label with the correct UN classification, and use certified carriers. Segregate from bases and reactive metals. Adhere to IATA/IMO/ADR regulations and supply Safety Data Sheets to all handlers for safe transport. |
| Storage | Store in a cool, dry, well-ventilated area away from direct sunlight. Protect from moisture. Keep the acidic etchant in tightly sealed, corrosion-resistant containers (HDPE, PTFE). Never store near bases, oxidizers, reactive metals, or flammables. Use secondary containment and clear hazard signage. Avoid incompatible materials, inspect regularly for leaks, and maintain original labeling. Always follow manufacturer and SDS storage guidelines. |
| Shelf Life | Shelf life is typically 6 months when stored tightly sealed in original container, protected from light, moisture, and contamination. |
In subtractive PCB fabrication, the acid cupric chloride system etches copper through a two-step oxidation of Cu0 by Cu2+ to form soluble cuprous chloride complexes, with re-oxidation of Cu+ to Cu2+ sustained by hydrogen peroxide or air injection under free HCl control. The working bath is prepared from electronic/EL-grade hydrochloric acid diluted to maintain free HCl at 1.5–2.5 M, cupric ion at 120–180 g/L, and chloride anion concentration not below 3.0 M to prevent cuprous chloride precipitation. Specific gravity is maintained between 1.28 and 1.36, oxidation-reduction potential at 520–560 mV vs Ag/AgCl, and copper concentration is measured by ultraviolet-visible spectrophotometry at 730–760 nm. The ORP value is used to meter electronic/EL-grade hydrogen peroxide 35% at a rate of 0.5–1.5 mL/L/h for each 10 g/L cupric ion increment above the target. In a horizontal conveyorized spray etcher with titanium or quartz heat exchangers, nozzle manifold pressure is set to 0.9–1.2 bar, bath temperature is held at 48–52 °C, and conveyor speed is adjusted to deliver 35–70 μm/min etch rate on 18 μm foil. Production-scale failure modes observed on these lines include etch rate collapse when ORP falls below 500 mV, cuprous chloride precipitation at spray tips when free HCl falls below 1.0 M, and resist foot undercut when cupric ion exceeds 180 g/L. Conductor width and spacing acceptances follow IPC-6012F Table 3-2 for Class 2 and Class 3, visual acceptance follows IPC-A-600H Section 3.6, and copper peel strength is verified by IPC-TM-650 2.4.8. Terminal finished products include multilayer motherboards, HDI server backplanes, automotive radar boards, and power module substrates.
| Cupric ion (g/L) | Free HCl (M) | ORP (mV vs Ag/AgCl) | Measured etch rate (μm/min) | Observed etch factor range |
|---|---|---|---|---|
| 120 | 2.0 | 530 | 35–45 | 2.0–2.6 |
| 150 | 2.0 | 540 | 45–60 | 2.6–3.2 |
| 180 | 2.0 | 550 | 50–70 | 2.5–3.0 |
The etch factor response shown in Table 1 cannot be captured by a single setpoint because panel loading, line speed, and bath copper inventory shift across production shifts. Etch factor is calculated as the ratio of vertical etch depth to lateral undercut; values below 1.8 usually require adjustment of conveyor speed or nozzle angle rather than acid concentration alone. On a production line with a 6 m effective chamber length, conveyor speed is commonly adjusted from 2.0 to 4.5 m/min, and the resulting line/space profile is verified by cross-section SEM after first article qualification. Published data for individual line configurations is limited because spray manifold oscillation frequency and tank recirculation design affect local ORP response.
The sulfuric acid–hydrogen peroxide micro-roughening bath is prepared by adding electronic/EL-grade sulfuric acid to deionized water to a working concentration of 90–120 g/L, then metering hydrogen peroxide 30% to maintain 20–35 g/L initially. Cupric ion is allowed to rise from 15 g/L to 30 g/L; beyond this window, hydrogen peroxide decomposition accelerates because dissolved copper catalyses radical formation, so stabilizers are dosed at 0.05–0.15 wt% of bath mass. The bath is operated at 28–35 °C in a horizontal spray module with 0.5–0.8 bar nozzle pressure and dwell time of 20–45 s, removing 1.0–2.0 μm of copper from foil or laminated innerlayers. The function is to replace passive cleaning with a controlled topological micro-roughening that raises peel strength after lamination, measured by IPC-TM-650 2.4.8, and dry film or solder mask adhesion, verified by cross-hatch tape testing under ASTM D3359-23. Incoming foil profile is controlled by IPC-4562, while solder mask adhesion after final finish is checked against IPC-SM-840D. Production equipment typically includes a two-stage cascade rinse, a dilute sulfuric acid predip before the micro-etch module, and conductivity-controlled rinse water at 10–20 μS/cm. Failure modes include local peroxide depletion at the centerline of wide panels due to poor manifold overlap, resulting in uneven roughening and subsequent resist nicking during plating. Terminal product types include multilayer PCBs, backplane assemblies, solder-mask-coated automotive boards, and copper-clad laminate surfaces prepared for dry film lamination.
In high-volume production, the micro-roughening bath is not operated indefinitely; cupric ion accumulation requires bleed-and-feed at 5–10 vol%/h to keep copper below 30 g/L, and hydrogen peroxide is added by peristaltic pump under oxidation-reduction potential control rather than manual batch dosing. Bath life between full dumps is constrained by dissolved solids and stabilizer degradation; production records show adhesive peel strength scatter increases when the bath exceeds 48 h of high-throughput operation without partial exchange. The process is less complex than cupric chloride etching, but the peroxide control loop remains the principal source of batch-to-batch variance.
On polyimide-based copper-clad laminates, the etch process must balance copper removal against degradation of the polyimide surface and the adhesive interface. The cupric chloride bath is diluted relative to rigid board operation: free HCl is held at 1.0–1.5 M, cupric ion at 80–130 g/L, and specific gravity at 1.20–1.30, with temperature reduced to 40–45 °C and ORP controlled at 500–540 mV vs Ag/AgCl. Etch rate for 18 μm rolled or electrodeposited copper is generally limited to 25–45 μm/min by conveyor speed and spray pressure 0.7–1.0 bar, preventing excessive undercut of fine traces. Flexible circuit production uses roll-to-roll or panelized formats; the etcher must provide low-tension transport, polyimide-compatible rollers, and spray impingement from both sides to avoid single-side puddling. After etching, the line includes a two-stage counterflow rinse with 0.5–1.0 M hydrochloric acid regeneration solution and an air knife dry section. Compliance for flexible printed boards is evaluated by IPC-6013C for performance requirements, IPC-A-600H for visual acceptance, and flexural endurance by IPC-TM-650 2.4.3. Terminal finished products include single-sided and double-sided flexible circuits, rigid-flex interconnects for automotive transmission sensors, wearable biosignal monitoring circuits, and foldable display interposers.
Double-sided spray etching of copper and copper alloy sheet uses the acid cupric chloride system to avoid ferric chloride residue that interferes with subsequent plating or welding. The bath is made up at cupric ion 80–150 g/L, free HCl 0.5–1.3 M, and specific gravity 1.20–1.32, with operating temperature 42–48 °C and spray pressure 0.8–1.4 bar. Sheet stock, typically 0.05–0.50 mm thick, is cleaned, laminated with photoresist on both sides, exposed by UV through a phototool, developed, and etched in a double-sided oscillating spray module. The process controls sidewall geometry through etch factor; for copper alloy stock the etch factor is generally held at 2.0–2.5, while for finer features it may fall to 1.5–1.9 depending on resist adhesion. Post-etch processing includes resist stripping in alkaline media, neutralization, and passivation. Compliance is governed by dimensional tolerance under ISO 2768-1:1989 class m for non-critical edges, surface texture under ISO 4287:1997, and base metal requirements under ASTM B36/B36M-19 for brass strip or ASTM B103/B103M-19 for phosphor bronze. Terminal finished products include semiconductor leadframes, EMI shielding plates, precision encoder disks, fine copper meshes, and spring contacts.
After copper pillar or redistribution layer plating, the exposed copper seed layer is removed by a sulfuric acid–hydrogen peroxide formulation whose selectivity against tin-silver caps is controlled by acid concentration, peroxide activity, and bath temperature. The solution is prepared at 5–10 wt% electronic/EL-grade sulfuric acid and 1–5 wt% hydrogen peroxide with an inhibitor; it is operated at 20–30 °C in a single-wafer spray tool or automated wet bench, removing 0.2–1.0 μm of copper seed within 30–120 s. The principal process conflict is galvanic attack: immersion in an acid-peroxide medium can cause accelerated copper dissolution adjacent to tin-silver bumps due to the potential difference between Cu+/Cu and Sn/Ag couples. To limit this, wafer handling avoids extended stagnant fluid contact, and the tool uses endpoint detection by optical emission or resistance monitoring rather than fixed time. Published data for this specific configuration is limited; qualification therefore relies on wafer-level test structures and cross-section SEM rather than vendor-reported etch rate alone. Compliance is evaluated under SEMI S2 for equipment safety, ISO 14644-1 Class 5 for cleanroom operation, and SEMI F47 for voltage sag immunity on automated etching equipment. Terminal finished products include copper pillar solder-capped flip-chip packages, wafer-level CSP interconnects, fan-out redistribution layers, and flip-chip packages.
For structures below 10 μm line width, etch process qualification typically uses two-dimensional cross-section measurement by SEM/FIB, and the acceptable copper loss is expressed as a maximum sheet resistance shift rather than a fixed etch depth. The bath is replaced or spiked based on hydrogen peroxide titration and acid normality; dissolved copper is controlled below 10 g/L to avoid precipitation and particle generation in the single-wafer tool. Recirculation is filtered to 0.05 μm absolute, and the chemical delivery system is constructed of fluoropolymer wetted components to avoid metal contamination.
| Standard / specification | Area of application | Verification method |
|---|---|---|
| SEMI S2 | Equipment safety and environmental performance | Risk assessment and third-party certification |
| ISO 14644-1 | Cleanroom particulate classification | Particle count at operational tool location |
| SEMI F47 | Voltage sag immunity | Equipment interruption test |
| IPC-TM-650 2.4.8 | Copper adhesion after etch | Peel strength on process coupons |
Thick copper heat spreader stock places elevated requirements on etch uniformity because local variations in spray impingement can produce channel width deviation and edge rounding that compromise thermal contact area. The acid cupric chloride bath for chemical milling of copper sheet 0.5–3.0 mm thick is maintained at cupric ion 120–180 g/L, free HCl 1.5–2.5 M, and specific gravity 1.30–1.38, with temperature at 45–52 °C and spray pressure at 1.0–1.5 bar. The workpiece is masked with a chemically resistant film or screen-printed resist and processed in a vertical or horizontal spray etcher; etch depths for thermal management features commonly range from 0.1 mm to 1.0 mm, so multi-pass scanning and intermittent rinse cycles are required to prevent localized heating. Post-etch processing includes caustic resist stripping, citric acid passivation at 50–60 °C, and deionized water rinsing to 5–15 μS/cm. Base metal conformance follows ASTM B152/B152M-19 for copper sheet, dimensional control follows ISO 2768-1:1989 class c, and surface cleanliness is evaluated by ion chromatography for chloride residue below 0.5 μg/cm². Terminal finished products include vapor chamber baseplates, high-power heat spreaders, water-cooled cold plates, and high-current copper busbars.
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For copper-metallized wafer-level packaging and high-density interconnect fabrication where post-etch cation residues on polyimide or modified epoxy dielectric must remain below 10 ppb, Acidic Etchant Electronic/EL Grade is specified as a formulated cupric chloride/hydrochloric acid solution with hydrogen peroxide regeneration. The product is not defined by a single molecular formula; commercial part numbers are vendor-specific and typically encode base chemistry, cupric ion concentration of 2.0–2.8 mol/L, free HCl concentration of 0.5–1.5 mol/L, and container size. The electronic/EL distinction is analytical rather than morphological: iron, nickel, chromium, and zinc burdens are controlled to levels compatible with ASTM D5127-13 Type E-1 water and are quantified by inductively coupled plasma–mass spectrometry according to ASTM D5673-16. Technical-grade cupric chloride etchants may carry 1–10 ppm total transition metals without a release certificate, making them unsuitable for exposed copper seed or barrier layers.
Reagent-grade hydrochloric acid and technical-grade cupric chloride differ from Electronic/EL Grade primarily in trace-metal distribution, particle burden, and packaging. The following comparison is drawn from electronic chemical procurement specifications rather than a universal datasheet; release limits are negotiated against device sensitivity.
| Parameter | Technical Grade | Reagent Grade | Electronic/EL Grade |
|---|---|---|---|
| Critical transition metals | Not guaranteed | ≤1 ppm total | ≤10 ppb per element |
| Particle count ≥0.5 µm | Not specified | Not specified | ≤25 particles/mL |
| Packaging | HDPE drum, single rinse | Polyethylene bottle | Cleanroom-rinsed fluoropolymer or HDPE |
| Certificate of analysis | Assay only | Assay and limited metals | Multi-element ICP-MS, particle count, density, free acid |
The consequence of using technical-grade material in fine-line etching is not a change in bulk copper removal rate; it is an increase in defect density at the resist/copper interface. On a continuous spray etcher with 0.8 mm fan nozzles and 1.2 bar nozzle pressure, metallic contamination precipitates as submicron particles once the bath exceeds 40 g/L copper loading, producing resist breaks and short-circuit scrap. Electronic/EL Grade is selected when line width falls below 50 µm and when downstream assembly requires no additional plasma descum before wire bonding. Batch-to-batch variance in technical-grade material is commonly observed as chloride-to-copper ratio drift, which moves the etch rate even when temperature and conveyor speed are fixed. By contrast, Electronic/EL Grade certificates of analysis report free chloride and cupric ion values for every lot, allowing the wet-process engineer to set the regeneration loop gain without re-qualification.
Because the hydrogen peroxide regenerant decomposes exothermically on rough transition-metal surfaces, the EL-grade recirculation loop is fitted with 0.1 µm PTFE membrane cartridges and the storage tank headspace is inerted or vented to maintain oxygen below 8% by volume. Production-scale spray tools hold bulk temperature at 50±2 °C using a shell-and-tube heat exchanger, and oxidation-reduction potential is controlled at 540±20 mV versus Ag/AgCl. Etch rate is therefore controlled by cupric ion regeneration rather than by free acid normality alone; cuprous precipitation at low potential is avoided, while excessive chlorine evolution at high potential is suppressed.
In ferric chloride etching, copper dissolution proceeds via reduction of Fe3+ to Fe2+, and the spent bath accumulates iron sludge that cannot be electrowon from dissolved copper without high cell voltage. In cupric chloride etching, the metal surface is oxidized by Cu2+ to form soluble Cu+ chloride complexes; the cuprous ion is then reoxidized by hydrogen peroxide according to 2 Cu+ + H2O2 + 2 H+ → 2 Cu2+ + 2 H2O. The absence of iron eliminates the viscosity rise associated with ferric hydroxide precipitation in rinse water and allows closed-loop copper recovery from the bleed stream.
Ferric chloride baths are typically operated at 40–45 °C and lose etch rate as Fe2+ concentration increases; cupric chloride lines can run at 50–55 °C with regenerant feed tied to ORP. The substitution is not universal: ferric chloride remains simpler for thick, noncritical copper removal because it does not require peroxide or chlorine regeneration. However, for 35 µm copper foil with line/space geometry below 50 µm, cupric chloride yields higher etch factor and lower lateral undercut when spray impingement is maintained at 1.0–1.5 bar and conveyor speed is reduced to 0.8–1.2 m/min. The spent cupric chloride bleed stream can be processed in electrowinning cells at 2–4 V and 30–40 A/dm²; ferric chloride spent baths cannot be regenerated in the same way because iron competes with copper deposition and forms a mixed cathode deposit.
Wafer bumping and redistribution-layer flash etching use the same EL-grade chemistry in single-wafer spray processors with 40–60 rpm wafer rotation and 0.5–1.0 mm nozzle spacing. The exposed copper seed thickness after sputtering is commonly 200–500 nm; endpoint is detected by optical reflectance rather than by timer because open area and seed thickness vary across the platen. In this application, the etchant must remove seed copper without attacking the nickel barrier or aluminum pad, which requires free HCl concentration to remain below 1.0 mol/L and bath temperature below 40 °C. Published data for this specific configuration is limited; qualification therefore uses a patterned 200 mm wafer with 25 nm Ti/ 300 nm Cu seed and scanning electron microscope inspection for barrier attack. Because the bath is used for seed removal, the endpoint signal is calibrated against coulometric copper thickness measurements rather than visual clearing. A bright dipping step is not required if the preceding copper plating bath was operated within 2–4 A/dm² and the seed layer was not annealed above 120 °C; above that temperature, cuprous oxide at the grain boundaries slows the initial etch and requires a higher free HCl concentration.
The certification package for Electronic/EL Grade acidic etchant defines metallic impurities by ICP-MS per ASTM D5673-16 and particle counts by optical particle counter calibrated to ISO 21501-4. Table 2 lists representative release limits for a formulated cupric chloride/hydrogen peroxide system; actual limits are part-number specific.
| Parameter | Method/Standard | Release Limit |
|---|---|---|
| Trace metals Fe, Cr, Ni, Zn | ASTM D5673-16 | ≤10 ppb each |
| Particle count ≥0.5 µm | ISO 21501-4 | ≤25 particles/mL |
| Free HCl | Potentiometric titration | 0.5–1.5 mol/L |
| Density at 25 °C | ASTM D4052-22 | 1.18–1.28 g/cm³ |
Because peroxide regeneration adds another contamination vector, the peroxide feed is specified as semiconductor-grade hydrogen peroxide with total oxidizable carbon below 10 ppm; otherwise organic stabilizers can adsorb on exposed copper and increase undercut variability. The filter housing is passivated with 10% nitric acid before installation, and the wetted surfaces are limited to PVDF or PTFE to prevent leached iron from accelerating peroxide decomposition. On a production line, a single failing pump seal can raise iron content above 25 ppb and shift the ORP set point by 20–40 mV, producing local overetch. The particle specification is not independent of packaging. Fluoropolymer drums are cleaned with ultrapure water to a final rinse resistivity of 18.2 MΩ·cm at 25 °C per ASTM D5127-13, and the filling line is maintained under ISO 14644-1 Class 5 conditions. A drum that is not rinsed to this level can contribute more than 100 particles/mL above the release limit, which appears as residual copper islands after final etch.
At 35 µm copper thickness, the etch factor depends on nozzle pressure, bath temperature, and cupric ion concentration more strongly than on total acid. A spray etch tool with 1.2 bar nozzle pressure and 50±2 °C bulk temperature typically produces an etch factor of 3.0–3.5 on 50 µm line/space features, equivalent to a lateral undercut of 10–12 µm per side. When the same bath is operated at 45 °C with 0.8 bar pressure, etch factor falls below 2.5 in the same geometry, and sidewall pitting becomes visible under 1000× optical inspection. The property cliff-edge is therefore the combination of low temperature and low impingement energy, not a single concentration threshold.
Electrolytic copper grain structure also influences the etch front; columnar grains with 0.5–2 µm width etch faster along grain boundaries, producing roughness measured as 0.8–1.5 µm Ra on the etched dielectric surface. This roughness is acceptable for dry-film lamination but may require a post-etch microetch if downstream solder mask adhesion testing demands roughness below 0.5 µm Ra. For copper foil with high elongation, the etch front also tracks rolling marks and oxide inclusions. A foil lot with tensile elongation below 3% may exhibit localized etch-rate acceleration of 10–15% along the rolling direction, producing open circuits in 50 µm lines even when the bath parameters are unchanged. The incoming foil specification therefore becomes part of the etchant process window; when the foil supplier changes, spray pressure and conveyor speed are re-qualified using a test coupon rather than relying on bath chemistry alone.
Acidic Etchant Electronic/EL Grade must not be mixed with nitric acid, because the combination forms aqua regia and releases nitrosyl chloride and free chlorine; it must also be kept away from strong reducing agents and aluminum features. In fabrication lines where relative humidity exceeds 60%, feed lines are heated to prevent condensation-induced hydrogen chloride fuming at low exhaust velocity. The etchant is stored in fluoropolymer-lined drums under nitrogen blanketing at 5–25 °C, and shelf life is defined by peroxide retention: once free peroxide concentration drops below 0.5 g/L, cupric chloride regeneration ceases and the bath must be reoxidized or replaced. Without recirculation, cuprous chloride can plate onto stainless steel immersion heaters, creating a short-circuit failure mode observed on production-scale wet benches.
