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3D X-ray inspection of LEDs for vehicle headlights
By Andreas Türk, AXI Product Manager, GÖPEL electronic GmbH
part of our daily lives. The auto- motive industry in particular has relied on this technology for a long time and is constantly push- ing it forward. LEDs have long been used
L
in vehicles not only to indicate various statuses or to illuminate displays. They are an integral part of headlights, indicators and rear lights, or in combination with optical fibers they conjure up a pleasant ambience in the passenger compartment. However, LEDs emit not only
light but also heat. Heat dissipa- tion is crucial for the service life of an LED. In earlier vehicle genera- tions, LEDs were installed with a classic component body and later- al solder connections. Currently, LEDs are manufactured as chip- scale packages (CSP LEDs), for example. This package no longer has an enclosure that extends beyond the light source. The con- nections for the anode and cath- ode are located directly under the housing body. Additional connec-
EDs have experienced a real triumph in recent years and are an integral
tions for heat dissipation (so- called heatsinks or thermal pads) are also located under the LED and are not visible from the out- side. This package reduces the LED form factor to a minimum, but requires new inspection con-
2D vs. 3D X-ray Voids (gas inclusions) in the
solder joints of an LED prevent the optimal dissipation of heat. The larger the void, the worse the heat dissipation and the shorter
vidually with the manufacturer and the end customer. To ensure optimum heat dissipation, vias (heat-conducting vias in the PCB) are placed directly under the LED, among other things. If the LED is X-rayed using convention- al 2D (vertical) or 2.5D (oblique) X-ray technology, the via and sol- der joint cannot be separated opti- cally. A check for via content is therefore not possible. Even if there are no vias under the LED, internal structures such as bond- ing wires themselves often inter- fere with the evaluation in the 2D X-ray image. The AXI system X Line — 3D
A board of LEDs used for vehicle turn indicators.
cepts for optical inspection in the PCB manufacturing process. Since the connections are con- cealed under the component, X- ray technology is the method of choice for inspection.
the service life of the LED. To date, there are no IPC limit values for the maximum permissible void content of an LED solder joint. According to the IPC, the limit value must be agreed indi-
from GÖPEL electronic GmbH uses fast, scanning 3D X-ray tech- nology for inspection. With 3D and the associated layer-by-layer inspection, the vias can be optical- ly separated from the solder joints above them. The 3D layered image of the
LED solder joint shows the voids without the disturbing influence of the vias or any bonding wires. The 3D reconstruction also elim- inates the typical X-ray perspec-
Continued on page 65
October, 2023
NH Research 9300 Battery Test System
• Programmable DC Power Supply • Regenerative DC Load • 1200 V, 100 kW - 2.4 MW • Battery Emulation • Fuel Cell Testing
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