The problem as it presented itself

The customer arrived with a working prototype and a production problem: the LEDs that passed the bench test were not the ones that survived the line. Nothing in the data was out of spec — the failures were spread across batches rather than concentrated in one lot, which ruled out a supplier problem and pointed at the process instead.

Three measurements separated the causes. First, forward voltage at a fixed low current across a sample of each batch, which showed whether the die set was consistent. Second, case temperature under the real drive condition, which showed whether the thermal path matched the assumption in the design. Third, the reflow profile logged on the line, which showed whether the assembly process stayed inside the qualified window.

The first two came back clean. The profile log showed the peak temperature sitting close enough to the limit that normal line-to-line variation pushed parts past it. This is the most common way a qualified component becomes an unqualified assembly, and it is invisible on the datasheet.

  • Measure the process, not just the part. A component that meets its specification can still be assembled outside its qualification.
  • Log the profile, do not assume it. Reflow profiles drift as boards and fixtures change.
  • Look at failure distribution first. Failures spread across batches point at the process; failures concentrated in one batch point at the supply.

Once the profile was corrected and re-qualified, the field return rate dropped to the level the component datasheet predicts. The component never changed — only the process around it.

For the irradiation end of the fast PCR instrument, if a Through hole Round LED with a diameter of 5/8/10mm is used, the optimized optical path is shown in Figure
1. The light emitted by the through hole LED first passes through a plano-convex glass lens, then filters the light through a filter, and finally converges the light into the optical fiber through a glass spherical lens. Plano-convex glass lens and filter, glass ball lens through optical fiber, numerical aperture NA = 0.56. Spacing between filter and glass ball lens = 3-5mm. The light spot on the fiber end face is shown in Figure
2. ZEMAX simulation found that the energy utilization rate of light is about 25.658%, compared with SMD LEDs (the energy utilization rate of light is about 85%)
PCR LED light path at the irradiated end through-hole LED diagram
Figure 1 Light path at the irradiated end (using Through hole LED)
Light spot on the fiber end face for PCR fluorescence excitation
Figure 2 Spot on the fiber end face
The above simulations are based on a wafer of medium to high power chips. Assuming that the thickness of the LED chip is 120 μm, all six sides of the wafer are illuminated. The wafer is in contact with the bottom of the holder’s reflective cup.
The drive current of the Through hole LED is expected to be 100mA. If it is greater than 100mA, the light intensity at the moment of lighting is high. If it is lower than 100mA, the light intensity is not enough to excite the fluorescence of low-concentration reagents, which will affect the sensitivity.
In terms of wavelength selection for through hole LEDs, the following are preferred:
1. Peak wavelength 430nm;
2. Peak wavelength 470nm;
3. Peak wavelength 520nm;
4. Color temperature 4000K full-spectrum white light;
5. Peak wavelength 630nm, or color temperature 3000K
6. The peak wavelength is 740nm.

PCR Optical System Design

PCR instruments require precise optical systems for fluorescence detection. Our through-hole LEDs with optimized emission wavelengths support real-time PCR and digital PCR applications with high signal-to-noise ratios.

LED Parameter Specifications

Our PCR-grade LEDs feature narrow spectral bandwidths (50mW), and viewing angle (15°-30°).

Through-Hole LED Options

Available in 3mm, 5mm, 8mm, and 10mm packages, our through-hole LEDs for PCR instruments offer excellent optical coupling with fiber systems. The round top design ensures uniform light distribution for multi-well plate illumination.

Application Guidelines

Our engineering team provides custom LED solutions for PCR instrument manufacturers. From UV LEDs for sterilization to high-power LEDs for illumination, we support your optical system requirements.

Excitation Spectrum Matching

PCR LED wavelength optimization for SYBR Green and TaqMan probes.

Thermal Stability

LED junction temperature control for continuous PCR cycling.

Intensity Calibration

Standardized LED output measurement for quantitative fluorescence.

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