- Oct 13, 2017 -
Classification and Selection of PCB Materials
1, we often choose FR-4 is not a material name
We often refer to the "FR-4" is a code for the level of fire-resistant materials, it means that the resin material through the combustion state must be able to self-extinguish a material specification, it is not a material name, but a Material grade, so the general circuit board used FR-4 grade material there are many types, but most of the so-called four-function (Tera-Function) of the epoxy resin plus filler (Filler) and glass fiber Made of composite material.
For example, our family now do FR-4 water green glass board black glass plate, he has a high temperature, insulation, flame retardant and other functions. So everyone in the choice of materials must be clear when they need to achieve what the characteristics of the material. So easy to buy their own products.
Flexible Printed Circuit Board (abbreviated FPC), also known as flexible printed circuit board, or soft printed circuit board. Flexible printed circuit board, is printed in the way, in the flexible substrate above the line design and production of the product.
Printed circuit board substrate has two main categories: organic substrate materials and inorganic substrate materials, the most used is the organic substrate materials. Different thickness of the PCB substrate used is different, such as 3 to 4 layers to use prefabricated composite materials, double-sided panels are mostly used glass - epoxy resin material.
2, select the plate, we need to consider the impact of SMT
Lead-free electronic assembly process, due to the temperature rise, the printed circuit board when the degree of bending increased, so in the SMT required to use a small degree of bending of the plate, such as FR-4 and other types of substrate. As the substrate after the expansion of the expansion and contraction of the impact on the components, will cause electrode stripping, reduce reliability, so the material should also pay attention to the material expansion coefficient, especially in the component is greater than 3.2 × 1.6mm to pay special attention. (150 ℃, 60min) and solderability (260 ℃, 10s), high copper foil bonding strength (1.5 × 104Pa above) and bending strength (25), high heat resistance (150 ℃, 60min) × 104Pa), high conductivity and small dielectric constant, good punching (accuracy ± 0.02mm) and compatibility with the cleaning agent, the other requirements smooth appearance, can not appear warping, cracks, scars and rust and so on.
3, PCB thickness selection
Printed circuit board thickness of 0.5mm, 0.7mm, 0.8mm, 1mm, 1.5mm, 1.6mm, (1.8mm), 2.7mm, (3.0mm), 3.2mm, 4.0mm, 6.4mm, of which 0.7mm and 1.5 mm thick PCB for the design of double-sided with gold finger, 1.8mm and 3.0mm for non-standard size. Printed circuit board size From the production point of view, the minimum board should not be less than 250 × 200mm, the general ideal size (250 ~ 350mm) × (200 × 250mm), for the long side less than 125mm or wide side less than 100mm PCB, easy Using puzzle. Surface assembly technology for the thickness of 1.6mm substrate bending amount of the provisions of the warp ≤ 0.5mm, under the warping ≤ 1.2mm. The permissible bending rate is usually 0.065% or less according to the metal material is divided into three kinds, typical PCB shown; according to the structure of soft and hard divided into three kinds of electronic plug-in to the number of feet, miniaturization, SMD and complex development The The electronic plug-in is mounted on the circuit board by pins and the pins are soldered to the other side. This technique is called THT (ThroughHoleTechnology) plug-in technology. So that the PCB board to drill holes for each pin, indicating the typical application of the PCB.
With the rapid development of SMT chip technology, multi-layer circuit board between the need for conduction, through the drilling to ensure that after plating, which requires a variety of drilling equipment. To meet the above requirements, at present, at home and abroad to introduce different performance PCB CNC drilling equipment. Printed circuit board production process is a complex process, it involves a wide range of processes, mainly involved in the field of photochemistry, electrochemistry, thermochemistry; in the manufacturing process involved in the process steps are more to hard Layer circuit board as an example to illustrate the processing steps. Drilling in the whole process is a very important process, the hole processing time is the longest, the hole position accuracy and hole wall quality directly affect the subsequent hole of the metal and patch processes, but also a direct impact on the printed circuit Board processing quality and processing costs CNC drilling machine principle, structure and function in the circuit board drilling methods commonly used CNC drilling method and laser drilling method, at this stage to use the most mechanical drilling method.