Precision PCB Fabrication, High-Frequency PCB, High-Speed PCB, Standard PCB, Multilayer PCB and PCB Assembly.
The most reliable PCB & PCBA custom service factory.
The size of a single fr4 pcb should be determined according to the overall structure of the whole machine. The size and shape of the fr4 pcb should be suitable for the production of the surface assembly line, and should conform to the size range of the substrate applicable to the printing machine and the mounting machine and the working width of the reflow soldering furnace. Due to the small size of SMB, in order to better adapt to SMT automated production, multiple boards are often combined into a single board, and several identical units fr4 pcb are consciously assembled in a regular way, and they are assembled into rectangular or square, which is called panel assembly.
The small size fr4 pcb can improve production efficiency, enhance the applicability of the production line and reduce the cost of tooling preparation. For single-sided mounting of printed boards, the mounting surface is on the same side. For double-sided full mounting without wave soldering, the double-sided panel can be used with half the front and half the back. The graphics on both sides are arranged in the same way. This arrangement can improve the equipment utilization rate (the investment can be reduced by half under the medium and small batch production lines) and save production preparation costs and time. The panels can be combined by means of V-shaped groove straight line segmentation, stamp hole, and gouging. The gouging is required to be accurate, uniform in depth, and has good mechanical support strength, but it is easy to be broken by the splitter or broken by hand.
The assembly of fr4 pcb with small identical printed circuit boards can also be carried out according to this principle, but attention should be paid to the compilation method of component tag number. The assembled printed circuit board is commonly known as "stamp" board.
1) The stamp board can be composed of multiple identical fr4 pcbs or different fr4 pcbs.
2) The maximum overall dimensions of the stamp board are determined according to the surface assembly conditions, such as the mounting area of the mounting machine, the maximum printing area of the printing machine, and the working width of the reflow conveyor belt.
3) The connecting ribs between the circuit boards on the stamp board play a role of mechanical support. Therefore, it should not only have certain strength, but also be easy to break to separate the circuit.
Red glue is a kind of polyene compound. Unlike solder paste, it will solidify after being heated, and its condensation point temperature is 150 ℃. At this time, the red glue starts to change directly from cyan to solid. Red gum has viscosity fluidity, temperature characteristics, cavity and humidity characteristics, etc. According to these characteristics of red glue, the purpose of using red glue in production is to make the parts firmly adhere to the surface of fr4 pcb to prevent it from falling. Because of the insulation of the red glue, the red glue must not stick to the pad.
It is mainly used in the following aspects in the actual production process:
1) Improper design of material or fr4 pcb, uneven tension during solder paste melting, which leads to deviation.
2) The components on the reverse side of the fr4 pcb are too heavy, and the components will fall off after the secondary melting of the front side through the reflow furnace.
3) If the strength of tin points formed by some components is not enough, use red glue to increase the strength.
UV is the abbreviation of Ultraviolet Raya in English (i.e. ultraviolet light). UV adhesive, also known as photosensitive adhesive, UV-curable adhesive and shadowless adhesive, is a kind of adhesive that can be cured only by ultraviolet light irradiation. It can be used as an adhesive. Ultraviolet (UV) is invisible to the naked eye. It is a section of electromagnetic radiation outside the visible light, with a wavelength of 10-400 nm. The principle of shadowless adhesive curing is that the photoinitiator (or photosensitizer) in the UV curing material absorbs ultraviolet light under the irradiation of ultraviolet light and produces living free radicals or cations, which initiate the monomer polymerization, crosslinking and branching chemical reactions, so that the adhesive can be converted from liquid to solid in a few seconds. Because of the insulation of the UV adhesive, the UV adhesive must not stick to the bonding pad. It is mainly used around the BGA in the actual production process to fix the BGA.
The storage and use process of red glue/UV glue is consistent with that of solder paste, which is only used as a supplement to solder paste. Solder paste can only be completed on the printing machine with steel mesh, UV glue can only be completed on the dispensing machine, and both processes of red glue can be used in fr4 pcb.
