| HS Code | 489569 |
| Appearance | clear blue-green liquid |
| Physical Form | aqueous liquid solution |
| Odor | sharp, penetrating hydrochloric-acid-like odor |
| Ph | less than 1 (strongly acidic) |
| Specific Gravity | approximately 1.20 at 20°C |
| Boiling Point | approximately 105°C |
| Freezing Point | approximately -20°C |
| Vapor Pressure | approximately 23 hPa at 20°C |
| Solubility In Water | completely miscible |
| Principal Active Etchant | copper(II) chloride (cupric chloride) |
| Acid Component | hydrochloric acid |
| Cucl2 Concentration | approximately 10-20 wt% |
| Hcl Concentration | approximately 5-10 wt% |
As an accredited PCB Etchant (TOK PCB Special 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 sealed high-purity 1L bottle, this Electronic/EL Grade PCB etchant ensures safe, precise use. |
| Container Loading (20′ FCL) | 20′ FCL loaded with palletized, UN-approved drums/IBCs of electronic-grade PCB etchant, securely braced, with chemical-compatible seals and hazard labeling. |
| Shipping | This chemical ships as hazardous material via ground transport only. It requires UN-rated packaging, proper labeling, and compliance with all applicable shipping regulations. Air freight is prohibited. Signature may be required upon delivery. Ensure recipient is authorized to receive corrosive/etchant chemicals. |
| Storage | Store in a tightly sealed original container in a cool, dry, well-ventilated area, away from direct sunlight, heat, and incompatible materials. Keep the container upright to prevent leakage, protect from moisture, and use secondary containment. Ensure proper labeling, segregate from food/chemicals, and follow manufacturer’s expiry and safety guidelines. |
| Shelf Life | Shelf life is approximately 12 months from manufacture when stored sealed in original container at room temperature, away from moisture. |
On rigid double-sided and multilayer printed wiring boards, TOK PCB Special Etchant Electronic/EL Grade is charged into an enclosed conveyorized spray etcher with oscillating nozzle manifolds above and below the panel transport plane. Where the bath is operated as an acidic cupric chloride system, free hydrochloric acid concentration is maintained between 1.5 M and 2.2 M, dissolved copper is allowed to rise from 120 g/L to 175 g/L, and oxidation-reduction potential is held at 520–580 mV against a Ag/AgCl reference electrode. Specific gravity is controlled to 1.30–1.38, and bath temperature is held at 48–52 °C. Double-sided spray pressure between 1.5 kg/cm² and 2.8 kg/cm² is delivered through 12–16 nozzles per chamber across four etch chambers; production lines typically circulate 800–1200 L/min through the spray manifolds. Under these conditions, 35 µm electrodeposited copper foil clears in 45–90 seconds, with measured undercut of 8–18 µm per side and an etch factor of 2.0–4.0 on dry-film resist patterns. The outerlayer artwork includes thieving rings and dummy copper areas to balance copper loading across the panel; without balanced loading, local ORP depression in dense areas reduces etch rate and leaves residual copper shorts. Finished conductors are accepted to IPC-A-600J Class 2 or Class 3 according to IPC-6012E, and cross-sections are prepared according to IPC-TM-650 2.1.1. Terminal products include automotive engine-control-unit boards, industrial PLC modules, and four- to eight-layer server mainboards with 75 µm/75 µm to 100 µm/100 µm outerlayer line/space.
Replenishment is metered by bleed-and-feed based on specific gravity and ORP drift rather than by fixed time. Drag-out from high-aspect-ratio dry-film features can reach 0.5–1.5 L per 100 panels, so the regenerator feed must compensate for both copper loading and chloride loss. The electronic/EL-grade specification limits sodium, iron, and nickel to low parts-per-billion endpoints because dissolved iron from stainless steel pump wear can act as a redox catalyst and destabilize ORP. In practice, iron concentration is kept below 50 ppm, and make-up water is monitored for chloride and sulfate background. If bath temperature exceeds 52 °C, dry-film resist adhesion loss appears as wedge-shaped undercut at the conductor foot; if temperature falls below 48 °C, etch rate drops 15–20% and conveyor speed must be reduced. The etch breakpoint is identified by the transition of the final chamber from high ORP to low ORP within 15 seconds, indicating that exposed copper has been removed without excessive attack on the sidewalls. Post-etch cleanliness is checked by IPC-TM-650 2.3.25 when the finished board must meet solder mask adhesion and wire-bonding requirements.
In SAP and mSAP process trains for HDI build-up layers, the etchant is diluted into a low-etch differential bath used to remove 3–5 µm of electroless copper seed layer from areas between electroplated fine-pitch traces. The process is run at 27–32 °C, with copper concentration maintained below 60 g/L and the etch amount controlled to 0.8±0.2 µm. This differential etch must clear the seed layer without reducing a plated circuit of 8 µm/8 µm to 12 µm/12 µm line/space by more than 1.0–2.5 µm per side. Vacuum or low-pressure flood modules with top and bottom meniscus contact are used because etch factor on thin seed layers can fall below 1.5 when spray impingement is non-uniform. Published data for this specific configuration is limited; production audits show conductor width loss increases rapidly if the etch amount exceeds 1.0 µm on test coupons. The etchant feed is filtered through 0.1–0.2 µm PTFE or polypropylene cartridges to remove particles that would block 10 µm gaps. Terminal parts include smartphone mainboard build-up layers and processor package substrates with 30 µm microvia capture pads.
| Differential etch variable | Operating range | Measured conductor width loss per side | Process note |
|---|---|---|---|
| Seed layer removal amount | 0.6–1.0 µm | 1.0–2.5 µm | Measured on 8/8 µm mSAP test coupon |
| Spray pressure | 0.8–1.5 kg/cm² | 0.8–2.0 µm | Higher pressure accelerates grain-boundary attack |
| Bath temperature | 27–32 °C | — | Above 35 °C promotes dry-film resist lifting |
Flexible printed circuits using rolled annealed copper foil laminated to 25 µm or 50 µm polyimide present a different grain structure than electrodeposited rigid board copper. The elongated grain structure retards vertical etch but can produce sidewall roughness when nozzle impingement angle exceeds 20° from vertical. On flex etch lines, nozzle pressure is reduced to 1.0–1.8 kg/cm², and the bath temperature is held at 42–48 °C. A typical process for 18 µm rolled annealed copper on 50 µm polyimide uses specific gravity 1.24–1.30 and copper content below 140 g/L. The resulting etch factor is commonly 2.0–3.0, with undercut values of 8–12 µm per side. Polyimide bond strength is maintained only if temperature remains below 50 °C; above that, the copper edges lift from the polyimide and allow etch solution wicking, which later causes delamination in thermal shock. Finished flex circuits are inspected to IPC-6013D Class 3, with cross-sections prepared according to IPC-TM-650 2.1.1. Terminal products include display driver flex assemblies, camera module links, and battery-management interconnects with 50 µm/50 µm to 75 µm/75 µm line/space. For 12 µm rolled annealed copper, the etch endpoint is judged by ORP shift rather than by visual color change because thin foil clears too rapidly for manual judgment. Where selective plating is present, free acid concentration must stay below 1.8 M to avoid attack on electroless nickel immersion gold pads, and drying after etch must be complete to prevent residual acid entrapment between polyimide layers.
Center-to-edge undercut variation on a 510 mm × 610 mm panel is measured by microsectioning conductor widths at nine coupon locations after etch. The target for conductor width reduction is ±10% of design width for Class 2 and ±5% for Class 3, as verified by IPC-TM-650 2.1.1. On a four-chamber spray etcher, center-to-edge undercut variation can exceed 6 µm per side if nozzle pressure and conveyor direction are unbalanced. The process conflict is that increasing spray pressure to raise center etch rate also accelerates edge etch of rail copper and outer columns; nozzle oscillation frequency and top-bottom flow ratio are therefore adjusted before pressure is increased. When top and bottom manifold flow rates are set to 1.2:1.0, panel edge-to-center etch rate variation is often held below 8%. Temperature control uses in-line heat exchangers with ±1 °C tolerance across the bath surface; thermocouples at pump suction and return sump prevent localized overheat from exothermic regeneration. Copper concentration and specific gravity are sampled every 4 hours, and replenishment is initiated with 0.8–1.2 L of concentrate per kilogram of dissolved copper etched from the panel, depending on drag-out. End products include edge-lit LED boards, power converter substrates, and server backplanes with 70 µm/70 µm to 125 µm/125 µm outerlayer conductors. For heavy copper starting foil of 70 µm or 105 µm, etch time increases to 120–240 seconds and undercut can reach 25–50 µm per side; this limits line/space below 150 µm/150 µm on heavy copper designs. IPC-6012E requires first article cross-section verification before lot release.
Copper alloy leadframes, SMT stencils, and precision encoder disks are etched from full hard or half hard copper and copper alloy strip with thicknesses between 50 µm and 300 µm. The electronic/EL-grade etchant is applied in photochemical machining lines where double-sided resist pattern covers the web and etching proceeds simultaneously from both faces. The process challenge differs from discrete panel etching because the workpiece is a moving web and dissolved copper accumulation increases density and viscosity, reducing spray penetration into fine slots. For a 150 µm thick leadframe strip, etch time in a high-pressure oscillating spray etcher is 180–360 seconds at 48–52 °C, and the etch factor is typically 1.5–2.5. Dry-film resist sidewall breakdown occurs if free acid concentration exceeds 2.5 M, and etch factor falls below 1.5 if bath copper concentration exceeds 180 g/L. The etchant is strained through 1 µm filters to remove insoluble copper hydroxide particles that can settle in 100 µm slot apertures and produce non-etched copper islands. Electronic/EL-grade feed with low sodium, iron, and nickel reduces insoluble precipitate formation and nozzle clogging. Terminal products include QFN leadframes, high-power LED leadframes, and copper SMT stencil sheets. Base material is checked against ASTM B152/B152M, and macroetch inspection of the etched cross-section follows ASTM E340. Published data for the precise etch rates of TOK PCB Special Etchant in photochemical machining of high-zinc brasses is limited; qualification on each alloy lot is therefore required before production.
After etching, chip-on-board and wire-bonding substrates retain etchant residues in the meniscus between conductor traces and in micro-roughness of the copper sidewall. The electronic/EL-grade specification constrains metal impurity levels because residual sodium, potassium, and chloride from etch chemistry can degrade wire bond pull strength and increase pad corrosion. The rinse train after the etch module uses four to six cascading deionized water stages with a final rinse resistivity of at least 18 MΩ·cm at 25 °C. Rinse water temperature is held at 40–50 °C to reduce surface tension and improve penetration under fine-pitch conductors. Final rinse chloride concentration is controlled to less than 10 ppb, and ionic contamination is measured by IPC-TM-650 2.3.25; the acceptance target for COB substrates is typically below 1.56 µg NaCl equivalent per cm². The process conflict is that high free acid concentration in the etch bath improves etch speed but increases post-etch chloride retention in solder mask-defined pad cavities; when acid concentration exceeds 2.2 M, the final rinse dwell time must be extended from 30 seconds to 45 seconds per stage. Wire-bond pull strength is tested by MIL-STD-883 Method 2011.9, with a minimum pull force of 8 cN for 25 µm gold wire; failures at the pad interface indicate insufficient rinsing rather than etch chemistry. End products include COB LED packages, smart card modules, and sensor wire-bond substrates with bond pad diameters of 80–150 µm. The use of electronic/EL-grade etchant with tight trace-metal limits reduces surface pitting that can occur when iron concentration in the etch bath exceeds 50 ppm. Similar post-etch cleanliness criteria apply to optical module substrates and RFID straps where wire bonding is performed directly over the etched copper pad.
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The PCB Etchant (TOK PCB Special Etchant) Electronic/EL Grade is specified for subtractive copper etching of copper-clad laminates. The product designation serves as the model identifier; no separate numerical model code is published in the referenced technical documentation. The material is supplied as an electronic/EL grade liquid etchant based on acidic cupric chloride/hydrochloric acid chemistry, with trace metallic impurities and particulate burden controlled for high-density interconnect and fine-line processing. Published formulation-specific assay data is limited; the process values below are representative for this class of electronic-grade cupric chloride etchants and should be confirmed against the shipping lot certificate of analysis before line conversion.
In enclosed spray etch chambers, the etchant is maintained at 48–52 °C (118–126 °F) with specific gravity 1.25–1.35 and free hydrochloric acid 1.5–2.5 N. The oxidation-reduction potential measured against a Ag/AgCl reference electrode is held at 500–600 mV to keep CuCl oxidized to CuCl₂ and prevent precipitation on copper surfaces. Spray nozzle pressure of 1.0–2.5 bar (14–36 psi) with full-cone polypropylene nozzles yields etch rates of 30–50 µm/min on copper foil in a 2.4 m-long production chamber. Under these conditions, 35 µm clad material clears at conveyor speeds of 1.2–1.5 m/min; 70 µm clad material clears at 0.6–0.8 m/min. Batch-to-batch etch-rate variance remains within ±5% when specific gravity, free acid, and ORP are controlled within the stated ranges. The processing window is narrow: free acid below 1.0 N initiates cuprous chloride precipitation, which blocks nozzles and increases undercut, while free acid above 3.0 N increases fume load and resist attack.
Because cupric chloride etch rate is mass-transport dependent, spray impingement uniformity is at least as important as bath composition. A rise in specific gravity above 1.35 indicates copper loading beyond the target window and requires withdrawal of spent etchant or adjustment with acidified deionized water. A fall below 1.25 reduces etch rate and can indicate overdilution or excess water ingress from rinse sections. The oxidation-reduction potential is used as an indirect measure of cuprous chloride accumulation: values below 500 mV suggest incomplete reoxidation and a risk of CuCl deposition, while values above 600 mV approach excessive oxidizer injection, which may generate chlorine gas and oxidize organic resists.
Copper dissolution proceeds through the reaction Cu + CuCl₂ → 2 CuCl. The cuprous chloride product is sparingly soluble and must be reoxidized to cupric chloride by chlorination, electrolysis, or metered oxidizer addition. In chlorination regeneration, chlorine is injected into the etchant circulation loop at a rate matched to copper loading. The oxidation reaction restores cupric chloride and consumes free hydrochloric acid; therefore free acid titration is not only a process variable but also a stoichiometric constraint. If free acid falls below 1.0 N, CuCl precipitation increases viscosity and forms nozzle-blocking solids. If free acid exceeds 3.0 N, the bath volatility and resist attack increase without proportional gain in etch rate. Electrolytic regeneration removes copper from the spent etchant while oxidizing cuprous species at the anode; this approach is favored in high-volume lines with continuous copper recovery cells.
Specific gravity is measured with a process hydrometer or inline density meter every 2 h on a production line. Free hydrochloric acid is titrated at the same frequency, and ORP is recorded continuously from a platinum electrode in the circulation loop. Copper content is determined by iodometric titration every 4 h, and trace metals are checked daily by inductively coupled plasma–mass spectrometry. The sampling frequency is derived from the drift behavior observed on production spray etchers, where a 0.01 specific gravity drift can correspond to a copper concentration change of 8–12 g/L, depending on free acid and temperature.
Electronic/EL grade supply specifies trace metal and particulate limits beyond commodity etchants. The typical cation impurity budget for this product class is controlled to <5 mg/L iron, <2 mg/L lead, <1 mg/L cadmium, and <5 mg/L chromium, with sodium and potassium below 10 mg/L each. Analytical verification uses inductively coupled plasma–mass spectrometry following EPA Method 6020B or equivalent. Dilution water is deionized to ASTM D1193-06 Type II or better, with resistivity above 1 MΩ·cm at 25 °C. The low-particulate requirement is relevant for HDI and fine-line processing because nozzle orifice diameters of 0.8–1.2 mm are sensitive to agglomerates; circulation loops are typically fitted with 0.5 µm absolute filters. Published lot-specific data for this specific product configuration is limited; these impurity values represent the electronic-grade cupric chloride class, not a certified certificate of analysis.
| Parameter | Acidic cupric chloride class (TOK PCB Special Etchant Electronic/EL Grade) | Ferric chloride | Sulfuric acid–hydrogen peroxide | Ammoniacal alkaline |
|---|---|---|---|---|
| Operating temperature | 48–52 °C | 40–50 °C | 35–45 °C | 45–55 °C |
| Copper loading | 150–180 g/L | 80–120 g/L | 60–100 g/L | 140–160 g/L |
| Regeneration | Chemical/electrolytic | Limited, high sludge | Difficult, exothermic decomposition | Chemical/electrolytic |
| Etch factor at 50 µm line/space | 2.5–4.0 | 2.0–3.0 | 2.5–3.5 | 2.0–3.5 |
| Resist compatibility | Dry-film/liquid photoresist | Photoresist | Photoresist | Alkaline-compatible photoresist; tin/lead resists |
| Waste treatment burden | Copper recovery by electrowinning | Iron-copper sludge | Copper sulfate recovery | Copper-ammonia complex treatment |
Direct comparison with ferric chloride and sulfuric acid–peroxide systems shows three operational differences. First, acidic cupric chloride is regenerable in situ by chlorination or electrolysis, so copper concentration remains stable and sludge generation is lower. Ferric chloride dissolves copper but forms mixed iron-copper sludge and cannot be economically regenerated. Sulfuric acid–peroxide etchant offers high etch rate and clean copper surfaces, but peroxide decomposition above 45 °C can produce runaway gas evolution and requires separate cooling. Second, because cupric chloride regenerates through CuCl oxidation, it maintains a stable ORP and etch factor over long production runs; ferric chloride loses oxidation potential as ferric iron is reduced. Third, the TOK PCB Special Etchant Electronic/EL Grade is not compatible with tin or tin-lead metallic resists, whereas ammoniacal alkaline etchants are used when those resists must remain intact. The selection is therefore driven by etch resist type, required fine-line geometry, and waste recovery infrastructure, not by etch rate alone.
Commodity ferric chloride is often supplied from steel pickling byproduct and contains appreciable iron, chromium, and suspended solids. The electronic/EL grade cupric chloride class uses copper as the active species, with iron controlled as an impurity to <5 mg/L. This distinction matters at the copper surface because residual iron can contribute to post-etch adhesion failures and can interfere with optical inspection. Cupric chloride does not leave the heavy iron oxide film sometimes associated with ferric chloride etching, and it is therefore easier to rinse from fine-line spaces. Sulfuric acid–peroxide etchants are attractive for clean copper surfaces but have lower copper loading and require stabilizer control to prevent exothermic decomposition. Alkaline ammoniacal etchants have high copper capacity and are compatible with tin-lead resists, but they introduce ammonia handling, copper-ammonia wastewater treatment, and additional nitrogen discharge limits.
| Control item | Specification | Test reference |
|---|---|---|
| Free hydrochloric acid | 1.5–2.5 N | Acid-base titration |
| Specific gravity | 1.25–1.35 | ASTM D891-18 |
| Copper content | 150–180 g/L | Iodometric titration |
| Oxidation-reduction potential | 500–600 mV vs Ag/AgCl | Platinum electrode |
| Iron | <5 mg/L | EPA Method 6020B |
| Particle count at 0.5 µm | <50 particles/mL | Light obscuration particle counter |
Acidic cupric chloride is selected when dry-film or liquid photoresist is used and where copper recovery by electrowinning is available. It is not appropriate for boards with exposed tin or tin-lead resists because the hydrochloric acid matrix dissolves tin and lead, causing resist loss and metallic contamination. For those applications, an ammoniacal alkaline etchant is substituted; the alkaline chemistry removes copper without attacking tin or tin-lead. The substitution is not trivial: ammoniacal etchants require closed-loop ammonia handling, copper-ammonia complex treatment, and different resist stripping sequences. In contrast, the TOK PCB Special Etchant Electronic/EL Grade is suited to fine-line acid etching of copper with organic resists in HDI production, where undercut control and controlled impurity levels matter. The boundary condition for choosing between the two etchants is the etch resist metal, not the substrate thickness.
Wetted materials for the TOK PCB Special Etchant Electronic/EL Grade in storage and etching equipment are titanium, polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene fluoride, and fluoropolymer-lined components. 316L stainless steel is not acceptable because free hydrochloric acid and cupric chloride cause pitting and stress-corrosion cracking at operating temperature. Heat exchangers are specified with titanium or fluoropolymer tubes; pump seals use PTFE or FFKM. Exhaust ducts must be polyvinyl chloride or polypropylene with capture velocity not less than 0.5 m/s at the tank lip to control hydrogen chloride vapor. The etchant is circulated at a flow rate that provides 2–4 tank turnovers per minute in spray sumps to prevent localized ORP depletion and CuCl precipitation. Published failure data from production lines indicate that nozzle clogging is most commonly caused by free acid excursions below 1.0 N, not by particulate alone.
Because actual etching performance depends on the etch resist type, panel thickness, copper thickness, and conveyorized spray chamber design, line qualification is required before changing from another etchant chemistry. For 50 µm line/space features, a stable production bath with good spray impingement typically develops an etch factor of 2.5–4.0. In a poorly balanced bath, undercut increases rapidly, and sidewall taper becomes non-uniform. Temperature above 55 °C accelerates resist lift and lateral etch, while temperature below 48 °C reduces etch rate enough to require slower conveyor speed or multiple passes. The most common production control failure is not a drift in copper content but a loss of free hydrochloric acid below the precipitation threshold, which then forces the line to stop for nozzle cleaning.
Spent etchant from this product class is treated by copper electrolysis or by precipitation as copper hydroxide with sodium hydroxide at pH 8–9. The copper sludge can be sent to copper smelters. Neutralization of hydrochloric acid with calcium hydroxide produces calcium chloride brine and copper hydroxide; this route increases sludge mass but is used when electrolytic recovery is not installed. Because the etchant contains no cyanide, no chromium, and no organic solvents, waste treatment is less complex than for ammoniacal or chelated systems. However, the high chloride content precludes direct discharge to surface water without chloride removal, and local sewer discharge limits commonly require chloride below 250 mg/L. The absence of intentionally added RoHS-restricted substances does not remove the obligation to verify each shipment against the current REACH Safety Data Sheet and local hazardous waste classification.
Storage should be in ventilated chemical rooms at 5–35 °C, away from alkaline materials, ammonia, hypochlorite, and strong reducing agents. Containers must remain closed to prevent hydrochloric acid vapor loss and moisture ingress. Contact with incompatible materials can generate heat, chlorine gas, or chloramine vapors. In production, the bath is replenished based on copper content and specific gravity; a stable bath does not require full dumps as frequently as ferric chloride systems. However, accumulation of non-etching cations and filter residue eventually requires partial or full bath replacement. Published product-specific bath life data for this configuration is limited; process engineers commonly monitor trace metal drift and chloride-to-copper ratio to determine the end of useful bath life.
Etching uniformity is assessed by cross-section and by electrical test after etching. Conductor width loss relative to artwork for 50 µm lines is typically 8–12 µm per side when the etchant is maintained within the stated window; this corresponds to an etch factor of 2.5–4.0. IPC-A-600 Class 2 and Class 3 acceptance criteria for conductor edge quality are verifiable after etching. These results assume optimized spray impingement, not static immersion; immersion etching with the same chemistry yields lower and more variable etch factors because mass transport is diffusion-limited rather than impingement-limited.
