Choosing the right LED aluminum PCB solder mask directly affects light output, thermal stability, and long-term reliability of an LED lighting product. PSR-4000 LEW7S / CA-40 LEW7S, a white alkaline-developable liquid photoimageable solder mask from Taiyo Ink, is one of the materials commonly specified for this application.
Why LED Aluminum PCBs Need a Different Solder Mask
An LED aluminum PCB isn’t just an insulating and protective layer — its surface also reflects light back through the LED package and helps dissipate heat generated by the chip. A standard solder mask that yellows or loses gloss under prolonged UV exposure and thermal cycling will gradually reduce surface reflectance, which shows up as reduced luminous efficiency and increased light decay over the product’s lifespan.
PSR-4000 LEW7S was formulated with this in mind: it’s white, halogen-free, sulfur-free, and specifically positioned for high resolution, high reflectance, and resistance to discoloration under UV rays and heat.
Key Technical Specifications
| Item | Specification |
|---|---|
| Main agent / Hardener | PSR-4000 LEW7S / CA-40 LEW7S |
| Mixing ratio | 85 : 15 by weight |
| Color | White |
| Viscosity | 160±15 dPas (cone plate viscometer, 5min⁻¹/25°C) |
| Solid content | 75±3 wt% |
| Specific gravity | 1.6±0.1 |
| Pot life | 24 hours, stored dark, below 25°C |
| Exposure energy | 500–700 mJ/cm² (under mylar film); 350–490 mJ/cm² (on solder mask) |
Reflectance Performance — the Metric That Matters Most for LED Applications
For an LED aluminum PCB, reflectance retention after reflow is arguably the single most relevant data point in the whole datasheet. Taiyo’s internal testing (KONICA-MINOLTA CM-2600d, 20μm solder mask on Cu, after 3 cycles of 285°C reflow) shows:
| Measurement | Initial | After Reflow (3x 285°C) |
|---|---|---|
| Y value | 87 | 85 |
| 460nm | 88 | 83 |
| 520nm | 87 | 85 |
| 640nm | 86 | 85 |
Reflectance stays within the 83–85 range across all measured wavelengths even after repeated high-temperature reflow — a reasonable indicator that the mask holds up under the soldering conditions LED aluminum boards typically go through, rather than only performing well on paper.
Process Conditions for Production
Based on the manufacturer’s recommended process range, typical parameters used in aluminum substrate production are:
- Printing: 100 mesh-count Tetron screen (adjustable 80–120 mesh)
- Exposure: 7kW metal halide lamp (ORC-680), 420 mJ/cm² reference value on solder mask, with an accepted range of 350–490 mJ/cm²
- Development: 1wt% Na₂CO₃ aqueous solution, 30°C, spray pressure 0.15–0.25MPa, developing time 45–75 seconds
- Post cure: 150°C / 60 minutes in a hot air convection oven
Cured film thickness should be kept within 10–20μm. Thinner coatings can reduce solder heat resistance and tin plating resistance; thicker coatings risk undercut and reduced tackiness. Since aluminum substrates conduct heat differently than FR-4, drying and curing windows should be verified against the specific oven and board load before locking in a production setting.
Reliability and Compliance
PSR-4000 LEW7S passed Taiyo’s internal cross-hatch adhesion test (100/100), 6H pencil hardness, 260°C/10sec solder heat resistance, and tape-peel tests after immersion in both acid (10% H₂SO₄) and alkaline (10% NaOH) solutions. Sulfur content testing (BS EN14582, 50ppm detection limit) came back not detected, and the product contains no intentional use of the six RoHS-restricted substances — relevant for LED products destined for regulated export markets.
As a PCB manufacturer in China, Guangzhou Mingen Electronics Co., Ltd. (CHNPCB) has manufacturing experience with LED aluminum PCBs using solder mask materials such as PSR-4000 LEW7S. Our standard PCB capabilities include single-sided, double-sided, and aluminum substrate PCBs, with laminate options such as KB6160 and a quality control process focused on maintaining consistent production parameters from batch to batch.
Beyond LED aluminum PCBs, PSR-4000 LEW7S is also compatible with Panasonic CEM-3 substrate PCBs, another material family that CHNPCB regularly works with.
CHNPCB has supplied LED aluminum PCB solutions to customers across Southeast Asia, the Middle East, and Europe. If you have questions about PSR-4000 LEW7S White Solder Mask application parameters or are looking for an LED aluminum PCB manufacturing partner, feel free to contact us at PCB@CHNPCB.COM.