Tg is the maximum temperature (° C) that the rigidity of the substrate can still be kept. At high temperatures, ordinary PCB material continues to produce softening, deformation, and melting phenomena. At the same time, they also show a sharp decline in mechanical and electrical characteristics, which affects the service life of the product.
What is high Tg printed circuit boards and the advantages of using high Tg PCB materials
When the temperature of a high Tg printed circuit boards rises to a certain threshold, the substrate will change from "glassy" to "rubbery." At this point, the temperature of a printed circuit board is referred to as the glass transition temperature.
The higher the glass transition temperature point, the higher the temperature requirements of the board during lamination and the pressed PCB board will be relatively hard and brittle, which will affect the quality of the mechanical drilling (if any) in the subsequent process and the electricity during use Sexual properties.
Tg point is the maximum temperature (°C) that the rigidity of the substrate can still be kept. That is to say, common PCB substrate material not only causes softening, deformation, melting and other phenomena at high temperatures, but also shows a sharp decline in mechanical and electrical characteristics.
Generally, the Tg board is above 130 ° C, high Tg point is always higher than 170 ° C, and the medium Tg is always higher than 150 ° C; usually, high-Tg PCBs are those that their Tg if higher than 170°C.
The advantage of high TG PCB is that with the development of science and technology, electronic products are developing towards high function and high multilayer, especially the development of high-density SMT technology. PCB is more and more dependent on the support of high heat resistance of substrate in terms of small aperture, fine circuit, and thin type. In addition, the mechanical strength, dimensional stability, adhesion, water absorption, thermal decomposition and thermal expansion of high TG materials are significantly better than ordinary PCB substrate materials at high temperature, especially after hygroscopic heating.
In the process of making PCB circuit boards, the thermal expansion coefficient of the substrate will have a certain impact on the PCB, such as tolerances, such as inter-layer alignment, etc. Today, the editor will focus on the thermal expansion coefficient of the substrate to the inter-layer alignment of the Pcb circuit board.
The substrate dielectric layer of the Pcb circuit board is formed by dipping a glass fiber cloth resin, and the CTE of the resin is much larger than the CTE of the glass fiber cloth. The CTE of the substrate composed of the two is not simply the "weighted sum" result of the resin CTE and the fiberglass cloth CET, but mainly the CTE of the fiberglass cloth plays the main role (X, Y direction). The experimental and application results show that the substrates composed of glass fiber cloth and resin mostly have CTEs between 13ppm / ℃ ~~ 17ppm / ℃ (X and Y directions), and the CTE in the Z direction is the CTE of the resin Influence the decision.
This is because the resin is dip-coated in glass fiber cloth, and then laminated with copper foil at high temperature to form a copper-clad substrate. In this process, because the resin melts and expands during high-temperature lamination, and then undergoes a curing reaction to cause size shrinkage, during the curing reaction and cooling process, in addition to the cooling shrinkage, there is also the shrinkage of the curing reaction. The glass fiber cloth in the middle prevents the resin from shrinking further. Therefore, the CTE of the cured substrate is between 13ppm/℃ ~ 17ppm/℃ (related to the type of resin and the type of fiberglass cloth, structure, etc.), rather than the simple between the fiberglass cloth and the well-known CTE " Weighted sum.
The base material of the Pcb circuit board, glass fiber cloth, is woven into glass fiber by glass mercerizing twisted into glass yarn. Fiberglass cloth is woven from warp yarns (large tension) and weft yarns (with little or no tension) and rolled into bundles, and then stretched to continuously dip resin (gluing) and dry to form prepregs. (B-stage adhesive sheet) state, and finally cut into a disc of prepreg and copper foil, and form a copper-clad laminate substrate by high temperature and high pressure.
It can be known that the residual stresses in the X, Y (or warp, weft) direction, or in all directions on the plane, formed by a series of mechanical and thermal treatment processes of this substrate are different.
In addition, the size of the board is always smaller than the size of the copper-clad laminate substrate (often cut into multiple pieces), and the influence of processing factors on the production process (temperature, humidity, machinery, etc.). Therefore, when the copper foil is removed by etching after the image transfer, the shrinkage dimensions in the plane are different, that is to say, the CTE in each direction in the plane is different. As a result, the deviation of the conductor pattern alignment between the various layers (or "chips") of the high-performance multilayer board is complicated, and it is difficult to calculate it with a simple CTE (or macroscopically using CTE, temperature and dimensional relationship). Accurate dimensional deviation of "chips" in each layer of the board. Therefore, the size measurement of each inner layer (chip) should be performed and then adjusted according to the size deviation level to improve the accuracy of the alignment between layers. This is a very careful and tedious operation. Fortunately, existing equipment such as AOL (Automatic Optical Inspection) can perform this task (including graphic defect inspection).
many times we are being asked how hot circuit board could get? What is the temperature resistance of PCB circuit boards? How is the heat resistance of PCB circuit boards tested? These are questions that customers often ask.
First of all, what is the maximum temperature resistance of the PCB board and what is the temperature resistance time? What if the temperature exceeds the normal temperature will its stability remain at normal?
With the rapid development of the electronics industry, especially electronic products represented by computers, the development of high-functionality and high-level multi-layers has increased the need for PCB substrate materials to have higher heat resistance.
High Tg refers to high heat resistance. The emergence and development of high-density mounting technology represented by SMT and CMT make PCBs increasingly inseparable from the substrate's high heat resistance in terms of small aperture, fine wiring, and thinness.
1.In terms of sheet material control, high TG is always used for the high precision product with higher quality requirements. PCBONLINE only use the material from internationally renowned brands, so it can make your product more stable.
2. Production experience: high TG always is a thick copper printed circuit board. The products are widely used in communication, medical treatment, aerospace, military industry, automobile，and computer peripheral products. Therefore, it is difficult to control in the production process, but PCBONLINE has rich experience in this field.
Inner layer technology: high TG, high speed, high frequency, thick copper, the thin dielectric layer and other special materials are used for the high-layer board, which puts forward high requirements for inner line production and graphic size control. For example, the integrity of impedance signal transmission increases the difficulty of inner line production. The smaller the line distance is, the more situations of the open and short circuit will be, slightly short circuit increases, the qualified rate becomes low; There are many signal layers in fine lines and the probability of missing AOI detection in inner layer increases. The thickness of inner core board is relatively thin, easy to fold and cause poor exposure, easy to roll when etched through the machine; Most of the high-layer board is system board, unit size is large, the cost of scrapping in the finished product is relatively high. PCBONLINE has carried out the technical transformation of the equipment and imported high-precision etching line equipment to improve the uniformity of etching, reduce the problems such as rough edges and unclean etching, so as to improve the quality.
B.Laminating technology: multiple inner core board and semi-solidified sheets are superimposed. Defects such as slide plate, lamination, resin cavity, and bubble residue are easy to be generated during the laminating process. In the design of the laminated structure, the heat resistance, voltage resistance, amount of glue and thickness of the medium should be fully considered, and a reasonable program of high layer board pressing should be set. Too many layers, expansion and shrinkage control and size coefficient compensation cannot maintain consistency; The thin insulation layer easily leads to the failure of reliability test between layers. PCBONLINE adopts material with different TG values in pressing, which cannot be set at the same stove. Common parameters board can not be laminated with special parameters board; To ensure the rationality of the given expansion and contraction coefficient, the performance of different board and semi-curing tablets is different, the corresponding board semi-curing tablet parameters shall be used for laminating, and the process parameters shall be verified for the special materials that have never been used.
C. Drilling technology: special board of high TG, high speed, high frequency, and thick copper are adopted, which increases the difficulty of drilling roughness and burr and defouling. Multiple layers accumulated the total copper thickness and board thickness, It is easy to break a knife when drilling a hole; In this regard, PCBONLINE has adopted the appropriate reduction of falling speed and rotation speed. Accurately measure the expansion and contraction of the board to provide accurate coefficients.
|Final board thickness||0.4-3.2mm|
|Min Drill Bit size||8mil|
|Hole size tolerance||
|Hole Position Tolerance||+/-2mil|
Line to PAD
Hard Gold Plating
SMD 40-2000u", GND 30-800u"
Au 1-5u", Ni 80-200u"
Au 1-50u", Ni 80-200u"