The reliability of LED lamp bead products is receiving increasing attention from manufacturers and users. As the basic constituent unit of the LED lamp bead, the quality of the LED lamp directly affects the reliability of the LED finished product. In practical applications, the dysfunction or even complete failure of the finished product often occurs due to the failure of the LED lamp bead. In recent years, a series of reliability problems such as color temperature drift, reduced lumens, and poor light output have been increasing due to discoloration of lamp beads, which has caused serious economic losses to many LED manufacturers and users.

First, the reason for the package

(1) Residual foreign matter in the encapsulant

     The appearance of the failed lamp bead is partially discolored and blackened. Uncovering the encapsulant, it was found that a black foreign matter was trapped in the encapsulant. The composition of the foreign matter was analyzed by scanning electron microscopy and energy dispersive spectroscopy (SEM & EDS) [5-6], confirming that the main components were aluminum (Al) and carbon (C). ), oxygen (O) element, also contains a small amount of impurity elements. Combined with the failure background of user feedback, the foreign matter is introduced during the packaging process.

(2) The encapsulant is chemically eroded to produce colloidal discoloration

     The failure product is a glass tube lamp, and the internal LED lamp strip is fixed on the glass tube by using a one-component room temperature curing silicone rubber, and the LED lamp bead on the lamp strip of the solid glue portion appears yellowish and dark. The failed lamp bead is made of silicone rubber. The elemental composition of the encapsulant was tested using SEM&EDS. It was found to contain more sulfur (S) than the normal lamp bead.

Second, the phosphor sedimentation

    When the lamp bead is assembled into an LED lamp and stored in the warehouse, the color temperature drift fails. The package rubber of the failed LED lamp bead changes from orange to light yellow. The IV characteristic test is performed, and the lamp bead can be normally lit, and the IV curve Normal, only the brightness of the light changes. Take some failed lamp beads, remove the encapsulant by mechanical unsealing, and find that there are transparent particles on the surface of the stent. The SEM&EDS test particle composition shows that it contains high content of strontium (Sr).

    In contrast, after the opening of the good lamp bead, the surface of the bracket is relatively clean, the main component of the surface is silver (Ag) and a small amount of carbon (C) elements, no sputum (Sr) element is detected, and in its encapsulant and bracket The strontium (Sr) and barium (Ba) elements were also not detected on the contact surface. By testing the cross-section components of the failed product and the good lamp bead encapsulant, the phosphors used in the two have the same composition, all of which are yttrium aluminum garnet (the main components are oxygen (O), aluminum (Al) and yttrium (Y). ) A phosphor mixed with yttrium silicate (mainly composed of carbon (C), oxygen (O), silicon (Si), strontium (Sr), barium (Ba), and calcium (Ca).

  Therefore, the failure of the LED lamp bead is caused by the silicate phosphor used to settle to the bottom of the encapsulant and the surface layer of the support, resulting in dispersion due to inconsistent light refraction laws, resulting in color temperature drift and lamp bead discoloration.