| HS Code | 344632 |
| Product Name | Silver Etchant |
| Chemical Composition | Nitric acid, phosphoric acid, acetic acid, water |
| Appearance | Clear colorless to pale yellow liquid |
| Density | 1.25 - 1.35 g/cm3 at 20°C |
| Ph | <1 |
| Boiling Point | Approximately 120°C at 760 mmHg |
| Solubility In Water | Fully miscible |
| Chemical Reactivity | Strong oxidizer; reacts with silver, bases, and reducing agents |
| Storage Conditions | Store tightly sealed in original container at 15-25°C away from incompatible materials |
| Safety Hazard | Corrosive; causes severe skin burns, eye damage, and harmful if swallowed |
| Etching Rate | Typical 1-5 µm/min depending on temperature, concentration, and agitation |
| Shelf Life | 6-12 months from date of manufacture if unopened |
As an accredited Silver Etchant factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Silver Etchant, 500 mL, packaged in a leak-proof HDPE bottle with child-resistant closure and clear corrosion hazard labeling. |
| Container Loading (20′ FCL) | 20′ FCL: drums of Silver Etchant securely palletized, blocked/braced, and loaded as full container load with proper hazardous cargo segregation. |
| Shipping | Silver Etchant is shipped as a corrosive, hazardous chemical. It requires leak-proof, acid-resistant packaging, proper hazard labeling, and compliance with dangerous goods regulations. Transport must avoid incompatible materials, ensure upright positioning, and include safety documentation. Handle with care to prevent spills, exposure, and environmental contamination during transit. |
| Storage | Store Silver Etchant in a cool, dry, well-ventilated area away from direct sunlight and incompatible materials. Keep the original container tightly sealed and upright, inside secondary containment to prevent leaks. Use corrosion-resistant trays and label clearly. Always separate from acids, bases, oxidizers, and flammable substances, and ensure access to emergency eyewash and spill supplies. |
| Shelf Life | Silver etchant shelf life is typically 6–12 months when stored sealed, cool, and protected from light. |
Within roll-to-roll fabrication of projected capacitive touch sensor arrays, sputtered silver films with thickness ranging from 50 nm to 150 nm are subtractively patterned on 125 µm polyethylene terephthalate or 0.7 mm soda-lime glass substrates. The acid bath is an aqueous admixture of 55–65 wt% phosphoric acid, 5–10 wt% nitric acid, 10–20 wt% acetic acid, and the balance deionized water at 15–18 MΩ·cm. This composition is selected because phosphoric acid moderates nitric acid attack while acetic acid reduces surface tension, enabling wetting of fine resist openings. Conveyorized double-sided spray etching equipment with PVDF-wetted tanks, PFA pipework, and quartz heaters operates at 38–42°C. The spray manifold uses 0.8 mm V-jet nozzles at 1.8–2.0 bar, delivering etch liquor to both web faces at a flow density of 4–6 L/min·m². At web speeds between 2 m/min and 4 m/min through a 3.2 m etch chamber, residence time spans 48–96 s. That interval clears 80–120 nm of evaporated silver while preserving exposed indium tin oxide or acrylic hardcoat layers. The primary process constraint is undercut control in isotropic wet etching: lateral silver removal advances at 0.7–1.0× the vertical etch rate. For a 100 µm line pitch, edge loss falls between 2 µm and 5 µm, so laser direct imaging compensation of 2–5 µm per edge is applied to the photoresist file. Rinse architecture uses two cascading deionized-water stages at 20–25°C, followed by a 3–5 wt% citric acid buffer at 35°C to clear residual silver nitrate and prevent polyester staining. Adhesion is checked by crosshatch tape pull after a 24 h age, per ASTM D3359, with acceptance at class 4B or higher. The bath is formulated without substances listed in RoHS Directive 2011/65/EU Annex II, and workplace exposure controls follow REACH Regulation EC 1907/2006 provisions for nitric acid mist. Line stoppages typically arise from nozzle clogging by crystallized silver salts and seal swelling in elastomer components; preventive replacement intervals are set at 400 h for nozzles and 1,000 h for wetted elastomer gaskets. Terminal parts include automotive center-stack touch films, tablet-sized sensor sheets, and white-goods capacitive interfaces.
Because silver/silver chloride reference electrodes require precise silver coverage before chloridation, sputtered silver films of 80–120 nm on corona-treated PET are etched into interdigitated electrode pairs using a cyanide-free iodide–triiodide bath. The working bath contains 0.5 M potassium iodide and 0.1 M iodine in deionized water, maintained at 28–32°C. Reel-to-reel immersion lines are configured with a 5.0 m dwell tank, 40 kHz ultrasonic agitation, and web speeds of 0.5–1.5 m/min, resulting in residence times between 200 s and 600 s. Published etch-rate data for sputtered silver in this bath class are generally in the 0.15–0.35 µm/min range at 30°C; the 100 nm silver layer clears within 30–60 s, but total dwell is extended to remove silver residue at pattern edges and ensure complete isolation between adjacent electrodes. Uniformity degrades once dissolved silver concentration reaches 20 g/L, because triiodide activity falls and etch rate slows by about 30%. Rinsing uses a three-stage cascade: deionized water at 25°C, then 0.05 M sodium thiosulfate to complex residual iodine stain, then final 18 MΩ·cm deionized water. Chloridation follows immediately in a separate bath containing 0.1 M potassium chloride, with a controlled potential of 1–2 V versus a silver/silver chloride reference, converting only the top 20–40 nm to AgCl. This stoichiometric control prevents complete conversion, which would raise impedance and reduce biosensor accuracy. Cytotoxicity of the finished electrode is evaluated per ISO 10993-5:2009, and production operations are controlled under ISO 13485:2016 quality systems. Bath change-out and replenishment are triggered by iodine depletion rather than silver loading alone; online absorbance at 350 nm serves as an indirect triiodide concentration monitor. Terminal products include single-use glucose strips, lactate test strips, and wearable ECG monitoring patches.
Thick-film silver conductors fired on 96% alumina substrates present a different etch problem because the film is 8–12 µm thick, densified, and filled with 2–5 wt% glass frit. Acidic silver etchant of the phosphoric–nitric–acetic class is applied by immersion at 45–50°C with 1.0 m/s solution agitation in a quartz-lined tank. Under these conditions the published etch rate for fired silver conductors typically lies between 0.2 µm/min and 0.5 µm/min, so removal of a 10 µm conductor can require 20–50 min. The glass frit does not dissolve and remains as a loosely adherent residue, requiring a post-etch ultrasonic rinse in deionized water at 40 kHz for 5–10 min. If the conductor contains silver-palladium alloy, the etch rate falls by roughly 40%, and palladium-rich residues may require a separate alkaline permanganate cleaning step. Etch depth is monitored by profilometry, with a target removal tolerance of ±1.0 µm across the substrate. Substrate attack is negligible on 96% alumina but can accelerate in etched via holes where glass phase is exposed. The process is used for rework of conductor shorts, trimming of resistor terminals, and opening of silver jumpers before final re-firing. Inspection criteria follow MIL-PRF-38534 class K visual and electrical requirements for hybrid microcircuits. Terminal parts include hermetic hybrid modules for avionics, high-reliability pacemaker circuits, and industrial pressure transmitters.
| Bath class | Typical working composition | Temperature range | Substrate compatibility | Key limitation |
|---|---|---|---|---|
| Acidic phosphoric–nitric–acetic | 55–65 wt% H₃PO₄, 5–10 wt% HNO₃, 10–20 wt% CH₃COOH | 38–42°C | PET, glass, alumina | Attacks exposed copper and nickel |
| Iodide–triiodide | 0.5 M KI, 0.1 M I₂ | 28–32°C | PET, polyimide, silicon | Iodine staining; triiodide depletion above 20 g/L Ag |
| Alkaline peroxide | 1:1:5 vol NH₄OH/H₂O₂/H₂O | 20–25°C | Silicon, glass, some polymers | Pot life 4 h; exothermic mixing |
Selective removal of silver spot plating from copper alloy leadframes is controlled by copper dissolution suppression, not by silver etch rate alone. Silver thickness after reel-to-reel plating ranges from 2.5 µm to 5.0 µm on C19400 copper alloy. Cyanide-free silver strip baths for this application typically combine an iodide or persulfate source with an organic triazole corrosion inhibitor at 0.5 g/L, maintaining pH between 8.5 and 9.5. Operating temperature is held at 45–50°C in an air-sparged immersion tank; strip time for 4 µm of silver falls between 10 min and 20 min. Supplier data for these formulations indicate copper etch rate below 0.05 µm/min, corresponding to a silver-to-copper selectivity above 100:1 under normal bath loading. The spent strip solution is filtered through 10 µm polypropylene cartridges to remove silver sludge, and dissolved copper is controlled below 500 mg/L to prevent triazole inhibitor exhaustion. After stripping, leadframes are water-rinsed, bright-dipped, and re-plated in a cyanide-free silver bath to restore spot thickness before molding. Wire bond pull strength after rework is verified per MIL-STD-883 Method 2011, with acceptance limits linked to 25 µm gold wire. Terminal devices include SOIC, QFP, and QFN packages for power management and automotive body electronics.
When finished PERC cells exhibit finger discontinuity or contact resistance excursions, reverse-bias photoluminescence inspection requires silver grid removal without damaging the silicon nitride passivation stack. The front-contact grid is screen-printed fire-through silver with finger width 30–60 µm and fired thickness 10–20 µm. A 10–15 wt% nitric acid solution in deionized water at 40–45°C is applied by vertical immersion with 0.5 m/s agitation for 30–60 s. This interval removes the silver fingers while the underlying silicon nitride layer remains intact due to its acid resistance under these conditions. Process control is by visual clearing and weight loss; cells are removed from the bath immediately after the last visible silver trace disappears because prolonged exposure increases pitting risk at busbar pads. After rinsing in 18 MΩ·cm deionized water and drying with filtered nitrogen, the stripped cell is evaluated by electroluminescence and reverse-bias photoluminescence to localize shunts and contact discontinuities. The spent etch solution is collected for silver precipitation and electrowinning under hazardous waste handling provisions of 40 CFR 261 in the U.S. market. Published etch rate data for industrial fired silver contacts in this specific configuration are limited; the values above are drawn from process control ranges rather than standardized test methods. Terminal output is diagnostic data for inline paste printer maintenance and firing furnace profile correction, not saleable product.
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Silver Etchant Type TFS is supplied as a ready-to-use, ferric nitrate–nitric acid etching formulation for selective removal of thin-film silver in semiconductor, photovoltaic, and hybrid microcircuit processing. The product is designated for immersion or spray etching of vacuum-evaporated, sputtered, and screen-printed silver layers, with a typical film thickness range from 0.2 µm to 25 µm. Published supplier technical data list a nominal etch rate of 2.5 nm/s for evaporated silver at 22 °C, a pH below 1.0, and a specific gravity of 1.10 at 25 °C. The formulation is designed to minimize attack on silicon dioxide, silicon nitride, nickel, and gold under controlled immersion times, while dissolving silver through a ferric ion redox reaction followed by nitrate regeneration of the active species. In production, the etchant is used for rework of photovoltaic front-side fingers, removal of silver from failed hybrid microcircuits, and delineation of silver thin-film patterns where a controlled etch front is required.
During dissolution, metallic silver is oxidized by Fe3+ to soluble Ag+, while Fe2+ is regenerated by nitrate species under strongly acidic conditions. Because the oxidizer is dissolved rather than gaseous, etched surfaces exhibit less pitting than equivalent nitric acid–only chemistries. The reaction rate is strongly temperature-dependent; process control within ±2 °C is recommended for low-undercut patterning. Film grain size and deposition stress also influence local etch rate, with sputtered films often requiring lower bath temperature or shorter dwell times than evaporated films of the same nominal thickness. Grain size is characterized according to ASTM E112-13 when etch-rate deviations are investigated.
Bath aging in Silver Etchant Type TFS is governed primarily by accumulation of dissolved silver, nitrate consumption, and water uptake from ambient humidity. As silver loading increases, the redox potential shifts and the etch rate on monitor wafers declines. Production baths are typically replenished before silver loading reaches the supplier-specified upper control limit; published data for this specific configuration is limited, but production-scale lines often establish an internal limit where the etch rate drops by more than 10% from the as-prepared value. Bath density and pH are monitored by titration and ion-selective electrode, respectively. Drag-out losses from cassette withdrawal add complexity because viscosity and density increase with silver concentration, altering drain time and uniformity on large substrates.
To maintain batch-to-batch stability, immersion equipment fitted with polypropylene or PVDF tanks, fluoropolymer cassette materials, and in-line 0.1 µm filtration is used to remove precipitated residues. Excessive agitation from air sparging is not recommended because it introduces dissolved oxygen and can accelerate precipitation of iron hydroxides. Temperature control at 20–35 °C is typical; above 35 °C, photoresist attack and undercut become measurable. Endpoint detection in automated lines uses optical transmission monitors or thickness-resistance probes. When the desired silver thickness removal is below 0.1 µm, timed immersion is supplemented by real-time detection because the etch rate in aged baths can vary by as much as 15% shift-to-shift.
Filtration and silver precipitation can be used to extend bath life, but the presence of ferric nitrate limits selective precipitation methods. Adding potassium hydroxide or sodium chloride is not recommended because it may precipitate iron and generate exotherms or hazardous by-products. The preferred waste-reduction approach is segregated collection of silver-bearing spent etchants for off-site reclamation, followed by neutralization of the acidic iron-containing fraction under a ventilated scrubber.
| Parameter | Value |
|---|---|
| Physical state | Clear light-amber liquid |
| pH | < 1.0 |
| Specific gravity | 1.10 at 25 °C |
| Nominal Ag etch rate | 2.5 nm/s for 500 nm evaporated Ag film at 22 °C |
| Recommended process temperature | 20–35 °C |
| Primary substrate compatibility | SiO₂, Si₃N₄, Ni, Au, hard-baked novolac photoresist |
| Storage shelf life | 12 months in sealed, acid-resistant container |
Because the acidic ferric nitrate system attacks copper, these values should be verified with a monitor wafer before production use on copper-bearing substrates. Selective silver removal on copper traces usually requires an ammoniacal chemistry or electrochemical protection.
Compared with dilute nitric acid, Silver Etchant Type TFS gives a more controlled etch front on evaporated silver due to the buffering effect of the ferric/ferrous couple. Dilute nitric acid produces a strongly exothermic surface reaction, with undercut excursions exceeding 2 µm per edge on 25 µm silver films when the bath temperature rises locally. The ferric nitrate system lowers the reaction enthalpy at the silver surface and maintains linewidth loss below 0.5 µm per edge for many hard-baked resist systems, provided immersion time is kept within the supplier-recommended window.
Ammonium hydroxide–hydrogen peroxide solutions etch silver through an oxidative complexation route that is useful where copper must be preserved, but they can release dissolved oxygen bubbles that adhere to fine features and create local cell-masking defects. Iodine–potassium iodide etchants are another alternative; they exhibit low photoresist attack but require thiosulfate or sulfite post-rinse to remove iodine residues and can contaminate downstream deposition equipment. The acidic ferric nitrate chemistry used in Silver Etchant Type TFS avoids iodine contamination and is compatible with standard deionized water rinsing and nitrogen drying.
| Etchant system | Typical pH | Ag removal rate | Undercut tendency | Resist compatibility | Representative use |
|---|---|---|---|---|---|
| Silver Etchant Type TFS | < 1.0 | 2.5 nm/s | Moderate; controllable by time and temperature | Good with hard-baked novolac resists | Controlled Ag patterning and rework |
| Dilute HNO₃/acetic acid | < 1.0 | High; strongly temperature-dependent | High | Moderate to poor | Bulk Ag strip |
| NH₄OH/H₂O₂ | 9–11 | Moderate | Low | Good | Ag removal from Cu-bearing substrates |
| Iodine/KI | 3–5 | Moderate | Low | Good | Ag patterning with post-rinse |
In front-side silver electrode rework for crystalline-silicon photovoltaic cells, the etchant is applied in a single-wafer immersion or spray module with a polypropylene process chamber and integrated deionized water rinse. For screen-printed silver fingers with a fired line width of 30–50 µm, removal must be complete before the etch front reaches the underlying silicon nitride anti-reflective coating. The Type TFS formulation is used at 22–25 °C in manual rework lines, with a total immersion time of 4–8 s for 10–15 µm fired silver fingers; the exact dwell time is determined by monthly monitor wafer testing because finger porosity and glass frit distribution vary by paste supplier.
Inline spray processing reduces localized heating and gives more uniform silver removal on large-format cells, but it requires exhaust ventilation because nitrogen oxides are released slowly from the acidic etch surface. The process window is often tightened to ±1 °C when cell antireflection coatings are thinner than 70 nm because over-etching of the silver finger edge can expose the underlying emitter. Published data for this specific configuration is limited; production lines therefore validate undercut with cross-sectional scanning electron microscopy after each bath change.
The product is classified as corrosive and oxidizer under transport regulations; it must be stored in an acid-resistant cabinet separated from incompatible chemicals such as ammonia, cyanides, and metal powders. Work areas require continuous ventilation and secondary containment. Because the solution contains nitric acid and ferric nitrate, the use of PVC piping is not recommended; PVDF, polypropylene, or PTFE wetted components are specified for recirculating etch lines. Equipment safety validation for spray etch modules follows SEMI S2-0721. Spent etchant is managed as hazardous waste with dissolved silver content typically in the range of 0.5–5 g/L depending on bath age. The pH is not neutralized with alkaline materials directly without temperature control because the exotherm can generate a nitric oxide plume.
Daily process control begins with a monitor wafer carrying 500 nm evaporated silver on silicon, immersed at 22 °C for 60 s, rinsed, and measured by four-point probe or profilometry. Acceptance limits are established relative to the supplier’s nominal rate: a drop below 2.0 nm/s or an increase above 3.5 nm/s triggers bath adjustment, replenishment, or replacement. The pH is measured with a glass electrode; density is checked with a hydrometer after temperature compensation to 25 °C. Batch records and etch-rate monitor data are maintained under ISO 9001:2015 control; material traceability extends to the supplier lot number and incoming inspection date. The bath is kept covered when idle to limit water absorption, which can raise pH and reduce etch rate.
Semiconductor failure-analysis laboratories employ the same formulation for removing silver epoxy attachments and package die metallization during cross-section preparation. The etchant is applied by drop or immersion in a fume hood; ultrasonic agitation is generally avoided because it can dislodge passivation layers and cause mechanical damage to exposed bond wires. In MEMS mirror release processes, silver is sometimes used as a sacrificial layer between silicon and gold. The ferric nitrate chemistry is preferred when the release etch must stop on a gold or silicon dioxide boundary, but etch time must be limited because fine-grain silver alloys may dissolve faster than standard evaporated films. Structured test coupons with embedded silver lines are used to confirm the endpoint before committing device wafers.
For surface-mount technology rework, the etchant can remove silver from solder pads after component lift-off, but it is not recommended for parts with exposed copper underplating because the chemistry attacks copper and can create pitting that reduces soldering reliability. Rinse is completed within 10 s of removal from the etch bath, and deionized water resistivity is maintained above 5 MΩ·cm. Nitrogen blow-off prevents water spotting, which can interfere with subsequent wire bonding or optical inspection.
