| HS Code | 400316 |
| Product Type | Liquid UV-curable photoimageable plating resist |
| Form | Viscous liquid, suitable for screen printing or roller coating |
| Color | Blue |
| Chemical Basis | UV-photosensitive alkali-soluble acrylic resin system |
| Photoactivity | Negative-working; exposed areas polymerize and remain as plating mask |
| Viscosity | Typical high-viscosity formulation, approximately 10–20 Pa·s at 25°C |
| Specific Gravity | Approximately 1.2 at 25°C |
| Non Volatile Content | Approximately 65–75% by weight |
| Developer Solubility | Unexposed areas develop out in dilute aqueous sodium carbonate solution |
| Stripability | Removable in warm 3–5% sodium hydroxide solution after plating |
| Plating Resistance | Withstands acid copper, nickel, and gold plating bath conditions |
| Adhesion To Copper | Strong adhesion to copper substrate without undercutting during plating |
| Resolution Capability | Supports fine line and space definition for PCB pattern plating |
| Thermal Resistance | Stable under conventional plating, drying, and stripping process temperatures |
| Electronic Grade Purity | Controlled low ionic and metallic contamination for electronic/EL applications |
| Shelf Life | 6 months when stored sealed below 25°C away from UV light |
As an accredited Plating Resist (Taiyo Ink Plating Resist) Electronic/EL Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaged in sealed amber bottles, this Electronic/EL Grade plating resist is supplied in 1 kg quantities for safe use. |
| Container Loading (20′ FCL) | Container Loading (20′ FCL): 20-foot full container load of Plating Resist (Taiyo Ink) Electronic/EL Grade, packed securely, moisture-proof, chemical cargo. |
| Shipping | This electronic-grade plating resist ships as a hazardous material via ground transportation only in approved, sealed original containers. It requires proper hazard labeling and cannot be shipped by air or internationally. Ensure compliance with local regulations and provide a safe, ventilated receiving area. Signature may be required upon delivery. |
| Storage | Store unopened or tightly sealed original containers in a cool, dry, well-ventilated area, ideally between 5–25°C (41–77°F). Keep away from direct sunlight, heat sources, sparks, and incompatible oxidizing agents. Avoid unnecessary exposure to UV light. Ensure containers are upright, protected from damage, and within labeled shelf life before use. |
| Shelf Life | Shelf life is typically 6 months from manufacture when stored in a cool, dark, tightly sealed container. |
Alkaline-strippable plating resist builds in Electronic/EL grade are applied at dry-film thicknesses of 10–20 µm on copper-clad FR-4, high-Tg FR-4, and halogen-free laminates before acid copper pattern plating. Pre-treatment typically includes a persulfate or sulfuric acid–peroxide microetch removing 0.5–1.0 µm of copper to generate mechanical topography, followed by deionized water rinsing above 18 MΩ·cm. Screen printing with 150–250 mesh polyester fabric or curtain coating establishes the resist layer; solvent flash-off is performed at 70–80 °C for 20–40 min. UV exposure through a phototool at 365 nm and 150–350 mJ/cm² crosslinks the carboxylated acrylate matrix in the exposed zones, while unexposed areas are developed in 0.8–1.0 wt% sodium carbonate at 28–32 °C for 60–120 s. The resulting resist sidewall angle, measured by cross-sectional scanning electron microscopy, is typically 45–75° depending on exposure energy and collimation. In acid copper pattern plating, electrolytes based on 60–110 g/L copper sulfate pentahydrate, 180–220 g/L sulfuric acid, and 40–70 ppm chloride ion are operated at 20–28 °C and 1.0–3.0 A/dm². The resist must withstand this strongly acidic medium for dwell times of 60–150 min without lifting, blistering, or surface plate-out. A critical processing boundary appears when plated copper thickness exceeds 25 µm: resist sidewalls may exhibit underplating unless the resist profile is slightly negative and phototool compensation is increased by 10–25 µm per side. Through-hole aspect ratios above 8:1 generally require pulse plating or periodic reverse waveforms rather than direct current to prevent dog-bone voids and to maintain throw power above 0.8 in the hole center. After copper deposition reaches 20–25 µm, the resist is stripped in 3–5 wt% sodium hydroxide at 50–60 °C with spray impingement for 2–5 min. Incomplete stripping becomes more likely when the resist has been heated above 100 °C during plating or drying, because decarboxylation and additional crosslinking reduce alkaline solubility. Adhesion of plated copper to the substrate is verified by tape peel testing in accordance with IPC-TM-650 2.4.1, and stripped surface cleanliness is checked by fluorescent dye inspection.
In electroless nickel/electroless palladium/immersion gold sequences, the plating resist remains in contact with acidic electroless nickel at 4.2–5.0 pH and 80–88 °C, followed by electroless palladium at 5.0–6.5 pH and 50–65 °C, and immersion gold at 80–90 °C. Resist surfaces must remain catalytically inactive; otherwise extraneous palladium nuclei and subsequent nickel deposition occur on non-plated traces, producing short-circuit defects. Electronic/EL grade material controls sodium, potassium, chloride, and calcium below 10 ppm each in cured film extracts because these ionic species can poison the palladium activator or accelerate electroless bath instability. A commonly observed failure mode on production lines is resist lifting at the copper interface during long-dwell electroless nickel; this is mitigated by microetching to 0.4–0.6 µm roughness, applying low-pressure surface activation, and avoiding post-develop hard bake above 110 °C. If the resist is under-cured at less than 150 mJ/cm², development leaves residual uncured monomers that bleed into the high-temperature electroless nickel bath, increasing organic carbon loading and triggering skip plating. Stripping after ENEPIG is performed in 3–5 wt% sodium hydroxide at 45–55 °C, but the stripping solution must not remain on immersion gold surfaces longer than 5 min because alkaline conditions can attack exposed copper at resist edges and widen line widths by 2–5 µm. Selectivity is judged by optical inspection at 50x–100x magnification for bridging and by X-ray fluorescence thickness mapping of palladium and gold on pads versus spaces. Background plating on resist surfaces is typically specified as not exceeding 5% of the pad thickness.
When polyimide flex cores and adhesiveless copper-clad laminates are moved through selective plating, the plating resist must not transfer extractable ions that reduce surface insulation resistance after final coverlay or soldermask lamination. Flex substrate construction of 12–25 µm polyimide with 12–35 µm rolled annealed copper exhibits lower tolerance to aggressive stripping than rigid FR-4; therefore the resist is applied at 8–15 µm dry thickness to limit stress at plated pad edges. Adhesion after exposure and development is typically required to remain at class 5B under ASTM D3359-17 Method B, with no edge lifting after plating at 1.5–2.5 A/dm². The resist must also tolerate short pre-plating cycles such as argon plasma cleaning, dilute sulfuric acid activation, and, in some flex processes, microetching of 0.2–0.4 µm on rolled annealed copper. After stripping in warm sodium hydroxide, residual sodium and chloride are critical because flex circuits are tested under 85 °C/85% RH and 50 V bias in accordance with IPC-TM-650 2.6.3.3; surface insulation resistance must remain above 100 MΩ. Dynamic flex endurance is verified separately per IPC-TM-650 2.4.3 at the final circuit stage, since plating resist is removed before bending; mechanical failure at that point is attributable to copper work hardening rather than resist residue. The key processing boundary in flex applications is that drying above 90 °C after development increases resist crosslink density and can produce cracked edges during the bending of thin polyimide cores, while insufficient drying leaves residual solvent that causes voids in subsequently plated copper.
Copper alloy leadframes such as C19400 and C7025 are selectively plated with silver, silver-copper, or copper-zinc alloy on bond fingers and die attach pads. The plating resist is applied at 15–30 µm thickness by reel-to-reel screen printing or photolithography and must survive electrolytic cleaning, acid activation, and silver plating at 1–4 A/dm² without electrolytic undercut. Silver spot plating from cyanide and non-cyanide electrolytes operates at 55–65 °C and 9–11 pH; the resist must maintain dielectric isolation and not leach organic compounds that produce tarnish or darkening. On production reel-to-reel lines, the most frequent failure is undercut at the resist edge caused by high chloride carryover from the activation step; this is controlled by rinse water conductivity below 10 µS/cm and by limiting the activation dwell to less than 60 s. After selective silver deposition of 1.5–4.0 µm, the resist is stripped in 3–5 wt% sodium hydroxide at 50–60 °C, typically in a spray section lasting 2–4 min. The bare copper die attach pad must remain free of silver contamination, commonly verified by SEM/EDX mapping with silver detection below 1 at% on the exposed pad area. The boundary for thermal exposure is set by the molding compound adhesion requirement: residues from incomplete stripping contribute to delamination under moisture sensitivity testing, and the exposed copper surface is therefore checked by water contact angle below 30° before epoxy encapsulation.
| Electrolyte system | Operating pH | Temperature | Current density | Typical dwell | Observed failure mode | Verification method |
|---|---|---|---|---|---|---|
| Acid copper sulfate pattern plate | <1 | 20–28 °C | 1.0–3.0 A/dm² | 60–150 min | Sidewall undercut, lifting at microetch topography | Optical inspection, IPC-TM-650 2.4.1 |
| Electroless nickel/ENEPIG | 4.2–5.0 | 80–88 °C | Electroless | 30–60 min | Organic bleed, skip plating | XRF thickness mapping, TOC analysis |
| Silver spot leadframe electrolyte | 9–11 | 55–65 °C | 1–4 A/dm² | 5–20 min | Undercut at resist edge, tarnish | SEM/EDX, XRF thickness |
| Sulfamate nickel electroforming | 3.5–4.5 | 50–60 °C | 0.5–2.0 A/dm² | 4–12 h | Thickness loss, TOC increase | Gravimetric film loss, TOC analyzer |
On etched stainless steel and copper alloy metal masks, the resist serves as a temporary etch barrier rather than a plating mask. Ferric chloride at 40–50 °C and cupric chloride at 45–55 °C attack unprotected metal through openings in the resist, and the resist must remain intact for 10–30 min to cut stock thicknesses from 0.05–0.30 mm. This chemical milling application requires resist thickness of 15–25 µm because etchants undercut the resist at the opening edge, producing a characteristic etch factor measured by cross-sectional inspection. Stainless steel 304 and 316 are particularly sensitive to chloride-induced pitting at the mask interface; therefore the Electronic/EL grade resist is selected for low extractable halide content and for adhesion to mechanically cleaned or acid-passivated surfaces. The developed resist is normally not subjected to thermal curing above 80 °C before etching, because higher temperatures increase sidewall brittleness and can cause fracturing when the chemical milling line operates at high spray pressure. After etching, the resist is removed in hot alkaline solution, and the etched features are inspected for edge burr, undercut, and residual organic film by dark-field microscopy and SEM/EDX. The same temporary-mask logic applies to beryllium copper alloy etching in cupric chloride; however, the alkaline stripping step must be followed immediately by citric acid neutralization to prevent beryllium oxide formation on the exposed metal surface.
Sulfamate nickel electrolytes used for electroforming operate at 50–60 °C, 3.5–4.5 pH, and 0.5–2.0 A/dm² for dwell times of 4–12 h. The resist is applied to mandrels or cathode fixtures to define non-plated regions. Under these conditions, resist films must withstand hydrolytic attack and maintain adhesion to stainless steel mandrels without releasing fragments into the bath. Published data for long-dwell plating resist performance in sulfamate nickel electroforming is limited; production qualification therefore relies on controlled bath exposure tests rather than extrapolation from short PCB plating cycles. A process validation typically plates nickel for 8 h at 55 °C and measures resist thickness loss, adhesion, and bath total organic carbon. Total organic carbon increase should remain below 200 ppm during the first 4 h to avoid pitting and compressive stress shifts in the electroformed nickel. The resist is removed in alkaline solution after electroforming; if stripped after nickel has built above 50 µm, mechanical stresses may crack the resist and release small fragments that block the bath filtration system. This failure mode is controlled by using filtration to 1 µm and by limiting the electroform thickness before resist stripping.
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Taiyo Ink Plating Resist Electronic/EL Grade is supplied as a negative-acting, photoimageable liquid resist formulated for temporary pattern plating masks on printed wiring board substrates. The product is specified in procurement documentation as Plating Resist (Taiyo Ink Plating Resist) Electronic/EL Grade. The Electronic/EL Grade designation differentiates the material from general-purpose screen resists and permanent solder masks by controlled extractable ionic contamination, finer filtration, and tighter rheological lot acceptance. The cured resist film is intended to survive acidic electrolytic copper, tin, and nickel plating baths and then be removed in an alkaline stripper without leaving residual organic film that would raise ionic contamination on the finished board.
Application of the liquid resist is performed by screen printing, double-sided spray coating, or curtain coating. Screen printing through polyester mesh of 100 to 150 threads/cm produces a dried film thickness generally between 8 µm and 25 µm. Spray coating is used where coverage over uneven copper topography must be more uniform than screen printing can deliver. After coating, the film is tack-dried in a convection or infrared tunnel to remove solvent and achieve a dry but photoreactive film. The exposure step is carried out with a UV source through a phototool; unexposed areas are developed in dilute aqueous sodium carbonate, leaving open channels for electroplating. After plating, the remaining resist is stripped in heated aqueous alkali.
Rheology is a primary electronic-grade control parameter. Viscosity at 25 °C is determined by rotational viscometer in accordance with ASTM D2196-20. Liquid photoimageable plating resists of this class commonly fall between 80 dPa·s and 180 dPa·s at 10 s⁻¹, with a thixotropic index of 1.8 to 3.0 between 10 s⁻¹ and 100 s⁻¹. The higher viscosity range is preferred for screen printing because it improves edge retention after print; the lower range is used for spray and curtain coating where leveling is critical. A lot with viscosity drift greater than ±10% from nominal should be rejected or recertified because wet film thickness will shift proportionally and alter both resolution and strip time.
Filtration and packaging are also part of electronic-grade control. The liquid resist is normally filtered through a final absolute filter rating of 5 µm or finer before packaging to remove agglomerates and gel particles. Packaging is typically light-blocking because the photoinitiator is sensitive to ambient UV and short-wavelength visible light. On high-volume production lines, air-driven diaphragm pumps or progressive cavity pumps transfer the resist from the container to the coating head. Peristaltic pumps with unsuitable tubing can introduce plasticizer contamination and should be avoided. Level sensors and recirculation loops should be constructed from stainless steel or solvent-resistant fluoropolymer components to prevent extractable contamination.
Resolution in the liquid resist system is controlled by dry film thickness, UV collimation, and development residence time. Free-radical photopolymerisation occurs after the coating has been tack-dried to a solvent-retention level at which the surface is sufficiently firm to prevent phototool sticking. For this class of liquid plating resist, a convective tunnel temperature of 75 °C to 85 °C for 15 min to 25 min is a representative process envelope. The temperature distribution across the panel should be held within ±5 °C because local solvent entrapment at the panel edges can form bubbles or lead to undercut during development. Excessive drying thermally advances the resist and raises the exposure dose required for complete polymerisation.
The exposure unit is a metal halide or LED direct-imaging system emitting in the 350 nm to 420 nm spectral region. A Stouffer 21-step wedge is used to set exposure dose; a clear step of 7 to 9 is a common target for this chemistry. Underexposure produces poor sidewall polymerisation, so the developed channel widens and the resist edge can lift during electrolytic copper plating. Overexposure reduces the minimum resolvable feature and creates a residual foot at the copper interface that slows alkaline stripping. Development is carried out in 0.8 wt% to 1.2 wt% sodium carbonate at 28 °C to 32 °C in a conveyorised spray chamber. The development breakpoint is normally maintained between 40% and 60% of the unexposed film thickness. Developer temperature below 26 °C leaves scum in fine channels; temperature above 34 °C attacks the exposed sidewall and causes channel widening.
Sidewall profile is also influenced by the divergence of the incident UV light and contact between phototool and resist. With a collimated source and intimate contact, the developed sidewall is commonly 5° to 15° from the vertical, with the opening slightly narrower at the top. If the parallel light divergence exceeds 5°, the bottom of the channel becomes wider and electroplated copper may extend under the resist edge. In fine-line applications, this underplating is a critical defect because it creates a lip that cannot be removed by subsequent etch and compromises conductor geometry.
Because published data for this specific Taiyo Ink Electronic/EL Grade configuration is limited to controlled supplier application trials, the numerical ranges above are class-level process envelopes for liquid photoimageable plating resists and are not guaranteed product specifications. Lot-specific processing parameters are supplied on the technical data sheet and certificate of analysis.
In comparison with laminated dry film photoresists and conventional solvent-borne screen resists, the Electronic/EL Grade occupies a distinct position with respect to resolution, conformality, and strip cleanliness. Dry film photoresists, typically supplied at 15 µm to 50 µm, achieve finer line/space resolution in the 15 µm to 30 µm range, but they require vacuum lamination and can tent poorly over heavy copper topography. Conventional solvent-borne screen resists are not photoimageable; their line/space capability is frequently limited to 100 µm or coarser and they cannot generate the vertical sidewalls required for pattern plating at fine pitch. The liquid photoimageable plating resist is applied directly over uneven circuitry and then photopatterned, giving a processing advantage in rigid-flex and build-up constructions where surface topography prevents uniform vacuum lamination.
| Process parameter | Electronic/EL Grade liquid resist | Dry film photoresist | Solvent-borne screen resist |
|---|---|---|---|
| Film thickness after drying or lamination | 8–25 µm | 15–50 µm | 15–40 µm |
| Minimum line/space capability | 40–75 µm class envelope | 15–30 µm class envelope | 100 µm or coarser |
| Application method | screen print, spray, curtain coat | vacuum lamination | screen print |
| Development | dilute aqueous sodium carbonate | alkaline or organic | not applicable |
| Stripping after plating | heated alkaline solution | strong alkaline or organic | solvent or mechanical |
| Ionic contamination control | electronic grade | film-dependent | general purpose |
The comparative values in the table are class-level process envelopes, not specification limits. Supplier certificates of analysis and application trial data should be used for acceptance of any particular production lot.
Electrolytic tin and nickel plating impose different process stress conditions. Acidic tin plating baths typically operate at 20 °C to 28 °C and 1 A/dm² to 3 A/dm²; the lower temperature is less aggressive, but the bath contains surfactants that may reduce interfacial adhesion. Sulfamate nickel baths operating at pH 3.5 to 4.5 and 50 °C to 60 °C are more demanding because elevated temperature accelerates diffusion of bath components into the resist. In such high-temperature electrolytic processes, dwell time should be minimized and resist thickness should be increased to maintain an effective diffusion barrier. Production experience indicates that edge lifting in sulfamate nickel is most often associated with excessive dwell time rather than inherent material failure.
Adhesion in electrolytic copper sulfate processing is governed by the micro-topography of the copper surface and the crosslink density of the exposed resist. Copper preparation uses a sulfuric acid/hydrogen peroxide or sodium persulfate microetch, removing 1 µm to 2 µm of copper and creating a matte surface. Cross-cut testing according to ASTM D3359-17 is used as a qualitative lot-release check; a 5B classification on the prepared copper surface is expected before plating. In an acid copper bath containing 55 g/L to 65 g/L copper, 80 g/L to 100 g/L sulfuric acid, and chloride at 40 ppm to 70 ppm, the exposed resist film is expected to withstand current densities from 2 A/dm² to 4 A/dm². Plating bath brighteners and carriers can migrate into the resist surface over extended dwell times; excessive carrier concentration softens the interfacial layer and can cause edge lifting. Bath temperature is usually maintained between 20 °C and 30 °C; excursions above 35 °C increase the diffusion of bath additives into the resist and should be avoided.
Stripping after plating uses an aqueous alkaline solution, usually 3 wt% to 5 wt% sodium hydroxide at 45 °C to 55 °C, sprayed at an impact pressure of 1.5 kg/cm² to 3.0 kg/cm². The resist swells and fractures into removable flakes rather than dissolving completely. Strip time is normally 90 s to 180 s. If the resist has been thermally over-baked or left in an acidic plating bath above 35 °C for an extended period, the strip time may increase to 5 min to 8 min. Residual film that cannot be removed within this window indicates over-cure; raising stripper temperature above 60 °C is not recommended because it may etch the copper surface without fully removing the crosslinked resist.
Incompatible process chemistries include strongly alkaline cyanide gold plating and aggressive solvent-based cleaning before stripping, which can harden the resist surface and reduce strip efficiency. The resist should not be diluted with amine-containing screen thinners because amine functional groups interfere with free-radical polymerisation and reduce crosslink density. For the same reason, amine-based stripper additives should be avoided when the remaining resist is to be removed in the standard alkaline process.
When the material is deployed in a high-reliability printed wiring board process, the supplier documentation package is typically verified against the following standards and regulatory instruments. The entries are informational and are not a substitute for lot-specific certification.
| Requirement | Standard or regulation | Significance for electronic grade |
|---|---|---|
| Ionic contamination after stripping | IPC-TM-650 2.3.25 | verifies extracted chloride is below acceptance threshold |
| Cross-cut adhesion | ASTM D3359-17 | classifies resist adhesion on prepared copper |
| Viscosity at 25 °C | ASTM D2196-20 | controls screen-print and spray application window |
| Heavy metal and flame retardant restriction | RoHS Directive 2015/863 | restricts lead, mercury, cadmium, hexavalent chromium, PBB, PBDE and four phthalates |
| SVHC declaration | REACH Regulation (EC) 1907/2006 | requires supplier declaration on substances of very high concern |
The Electronic/EL Grade is not intended as a final solder mask or permanent dielectric. It is a temporary plating mask that must be removed before final surface finish and electrical test. Storage should follow the supplier’s specified temperature and shelf-life parameters because solvent loss and thermal polymerisation shift viscosity and exposure speed. At relative humidity above 60% and a board surface temperature below the dew point, the wet film may absorb moisture and develop a hazy surface; pre-drying of substrates is required under those conditions. The material should not be processed in the same developer or stripper as permanent solder masks if the bath is not dedicated, because dissolved permanent-mask components can alter the plating resist’s development and stripping window.
