1.FR-4 is not a kind of material
“FR-4” is a kind of flame retardant material grade code, meaning it represents is a kind of material specification that the resin material after combustion state must be a self extinguishing, so it isn’t a kind of material name, but a kind of material level, and there are many kinds in FR4 level material currently used on the circuit board, but most are based on the so-called four function (Tera-Function) of epoxy resin and filler (Filler) and composite material made of glass fiber.
In fact, the FR4 glass fiber board has high temperature resistance, insulation, flame retardant and other functions. So when you choose materials, you must make clear what material you need to have characteristics. Only in this way can you buy the products you need.
2.Effect of sheet metal on SMT
In the process of lead-free electronic assembly, the degree of bending of printed circuit board will increases when heated due to the increase of temperature, so it is necessary to use the plate with small bending degree in SMT, such as FR-4 and other types of substrate. Because the substrate heat expansion effect of stress on the element, which will cause the electrode stripping and reduce the reliability, so the expansion coefficient of the material should be noted when choosing material, especially should pay special attention to more than 3.2 x 1.6mm in the element. In surface of PCB Assembly technology in PCB should have high thermal conductivity, excellent heat resistance (at 150 60min) and weldability (at 260 10s), high bonding strength of copper foil (1.5 x 104Pa) and flexural strength (25 * 104Pa), high conductivity and low dielectric constant, good flushing discretionary (accuracy + 0.02mm) and detergent compatibility, additional requirements may not be smooth, warping, cracks, scars and rust etc.
There are many pcb thickness including 0.5mm, 0.7mm, 0.8mm, 1mm, 1.5mm, 1.6mm, (1.8mm), 2.7mm, (3.0mm), 3.2mm, 4.0mm, 6.4mm, 0.7mm and 1.5mm PCB is used to design the thickness of the double panel with a finger, 1.8mm and 3.0mm for non-standard size. Considering from the perspective of production, the smallest size of circuit board should not be less than 250 * 200mm, the general ideal size (250 ~ 350mm) * (200 * 250mm), the long side is less than 125mm or less than 100mm PCB wide, easy using puzzle mode. The surface mount technology of thickness 1.6mm substrate bending is specified on the warpage of less than 0.5mm, less than 1.2mm under warping. The bending rate is usually allowed in 0.065% are divided into 3 types according to the metal materials, according to the structure of hardware and software is divided into 3 kinds, electronic plug-in to high pin count, miniaturization, SMD and complex development. The electronic plug-in is installed on the circuit board through the pin and welding the foot to the other side. This technology is called THT (ThroughHoleTechnology) plug-in technology. Thus, the drill hole of each pin should be drilled on the PCB board, indicating the typical application mode of the PCB.
With the rapid development of SMT patch technology, multilayer circuit boards need to be connected, which is guaranteed by electroplating after drilling, which requires a variety of drilling equipment. In order to meet the above requirements, at present, at home and abroad to introduce different performance of PCB CNC drilling equipment. The production process of printed circuit board is a complex process, and it involves a wide range, mainly involved in the field of light chemistry, electro-chemistry, chemical;
Also its process steps is much more in the manufacturing process, with hard multilayer circuit board as an example to illustrate the process. Drilling is a very important process in the whole process, hole processing time is the longest, and the metal patch process such as position accuracy and quality of hole wall hole directly affects the hole, but also directly affect the common method principle, processing quality and processing costs of CNC drilling machine of the structure and function of printed circuit board drilling on the circuit board are CNC Mechanical drilling method and laser drilling method, at the present stage, the most frequently used method for mechanical drilling.