structure
The basic semiconductor digital tube is composed of seven strip-shaped light-emitting diode chips arranged as shown in Figure 12. Can realize display of 0~9. Its specific structures include "reflector type", "strip seven-segment type" and "monolithic integrated multi-digit type", etc.
(1) Reflector-type digital tubes are generally made of white plastic into a seven-segment housing with a reflective cavity. A single LED is attached to a printed circuit board aligned with the seven reflective cavities of the reflector. The bottom of each reflective cavity The center position is the LED chip. Before installing the reflector, use pressure welding to connect φ30μm silicon aluminum wire or metal leads between the chip and the corresponding metal strips on the printed circuit. Drop epoxy resin into the reflector, and then attach the printed circuit with the chip. The plate is aligned with the reflector and then cured.
There are two types of packaging methods for reflector-type digital tubes: air sealing and solid sealing. The real sealing method uses epoxy resin with scattering agents and dyes, and is mostly used for one- or two-position devices. The air sealing method is to cover the top with a filter and a uniform light film. In order to improve the reliability of the device, transparent insulating glue must be applied to the chip and the bottom plate, which can also improve the light efficiency. This method is generally used for digital display (or symbol display) of more than four digits.
(2) The strip-shaped seven-segment digital tube is a hybrid packaging form. It is to divide the gallium phosphide or gallium phosphide wafer that has made the tube core into one or several LED light strips, and then stick the same seven strips on the Japanese-shaped "Kovar" frame and use pressure welding to The process connects the inner leads and then encapsulates them with epoxy resin.
(3) The single-chip integrated multi-digit digital display is based on a luminescent material substrate (large wafer). It uses integrated circuit technology to produce a large number of seven-segment digital display graphics. Qualified chips are selected by dicing and affixed to the printed circuit. On the board, use a pressure welding process to draw out the leads, and then cover it with a "fisheye lens" shell. They are suitable for use in small digital instruments.
(4) The production method of symbol tube and rice tube is similar to that of digital tube.
(5) Matrix tubes (light-emitting diode dot matrix) can also be produced using a process similar to that of a monolithic integrated multi-digit digital display.
