Epoxy resin sealing board is also called epoxy board, and its appearance is shown in Figure 1. It is mainly composed of battery, printed circuit board and epoxy resin. The specific size and shape are determined according to the needs of the product. The structure is shown in Figure 2. Since the power of the epoxy resin sealing board is very small, the battery slices used in it are made by cutting the complete battery slices into strips. The length and width of the strip cell, that is, the area of the cell, determines the output current of the module, and the number of series connected determines the output voltage of the module. Generally, 4 modules are connected in series for 1.2V battery charging, 7~8 modules are connected in series for 2.4V battery, and 11 modules are connected in series for 3.6V battery charging. The plastic cover of the epoxy resin sealing board assembly faces outward to receive sunlight, and the sun shines on the battery through the plastic cover. And the emitted electricity is led to the back of the circuit board through the positive and negative leads, and then connected to the corresponding circuit or battery through the leads.
Figure 1 – Shape of epoxy resin sealing board Figure 2 – Epoxy resin seal board structure diagram
The production process of epoxy resin glue sealing board modules is basically manual operation. The cells are pre-cut with a laser scribing machine according to the required size, and the manufacturing steps are as follows.
(1) Solder the cut strip cells in series with interconnecting strips-plus and minus, and fix them on the printed circuit board with black double-sided tape.
(2) Pass the positive and negative leads through the lead holes on the printed circuit board and weld them to the circuit copper foil on the back of the circuit board, and then put them on the horizontal support one by one and wait for the glue to be poured.
(3) Mix the two-module epoxy resin glue according to the ratio of 2 to 1 and adjust it evenly (Be careful not to mix too much at one time, otherwise it will not be used up at a time, it will thicken in ten minutes and cannot be used), pour an appropriate amount of glue (average 0.15g/cm2) on the surface of each module to spread it out naturally. The glue on the surface of the module should be even and full, and the glue should be patched up if the glue is too thin.
(4) Put the glued modules into a vacuum drying oven for 1 minute, and then dry them at 70°C for 30 minutes or dry them naturally in a dust-free environment for 24 hours.
(5) Remove the excess rubber particles around the modules, wrap them with a film to prevent friction and damage the surface smoothness and transparency, and then pack them into the packaging box to make the finished product.
Epoxy resins are widely used as adhesives, and the product forms are single-module, two-module or powdered resins. The epoxy resin adhesive used in solar cell modules is usually a two-module liquid, and it is ready for use when it is used. Epoxy resin has a high degree of adhesion, simple process and low material cost, but it has poor aging resistance and is prone to aging and yellowing. Therefore, it is very important to improve the aging resistance of battery modules encapsulated by epoxy resin. In addition, as a solar cell packaging material, high humidity resistance and air tightness are required. Epoxy resin is a polymer material, and its molecular spacing is 50~200nm, which greatly exceeds the volume of water molecules, and the penetration of water can reduce the service life of solar cells. Secondly, when the solar cell module is encapsulated with epoxy resin, due to the different expansion coefficients of different materials, internal stresses such as improper material configuration and process will generate internal stress during the production process, which may cause various defects such as reduced module strength, cracks, package cracks, voids, and peeling, which will seriously affect module quality. Since the service life of epoxy resin sealing board modules is only 2 to 3 years, only some small modules below 1W still use epoxy resin encapsulation, and larger modules no longer use this process.