Reviewing the history of FR-4 board. For many years, some in the industry who have always thought that FR-4 board has such as obsolete will do, so instead of researching alternative to other high performance. Every time when the specifications have increased, the plate must be best to suppliers, to meet customer demand. In recent years, the most obvious development trend of the market
That is a large increase in demand for high Tg sheet. In fact, many of the industry's understanding of the issue of Tg, it seems that the high Tg that has a high efficiency, or better reliability. One of the main purpose of this paper, the characteristics of next generation FR-4 board should have, has a non TG can fully express, so he put forward more resistant to heat should have the new specifications, for lead-free soldering challenge.
Two, leading the industry trend of substrate specifications
A number of industry trends in the process, which will lead to the re formulation of the city and the use of these trends, these trends include multi laminate design trends, environmental regulations, as well as the demand for electricity, etc.:
Design trend of 2.1. multi - wide plate
Currently one of PCB design trends is to improve the wiring density, desire of this goal has three: first, cut the line width and distance, the unit area can accommodate more more intensive wiring; followed by an increase in the number of layers of the circuit board; finally, reducing the aperture and pad size.
However, when the unit area of the line more and more time, the working temperature is bound to rise. In addition, increasing the number of circuit boards, it is bound to make the completion of the synchronous plate thickness. Otherwise, it can only be matched with a thin dielectric layer to maintain the original thickness. PCB is thick, the hole wall caused by heat accumulation heat stress will increasingly increase, thus making the Z direction becomes larger thermal expansion effect. Selection of the thinner dielectric layer, it means must use rubber content more substrate and film; but gum content of more, will cause through aperture Z direction of thermal expansion and stress to increase. Furthermore, reducing the through hole aperture, unavoidable and the aspect ratio becomes large; therefore, in order to ensure the plated through hole of reliability, the substrate must have lower thermal expansion and better thermal stability, not only lost by the wayside.
In addition to the above factors, when the circuit board assembly component density increased, then the layout of the guide holes will also be arranged more closely. But this will make the www.pcblover.com glass leakage of the situation more tense, even in the hole wall between the glass fiber bridging phenomenon occurs, resulting in a short circuit. This anode of filamentous leakage phenomenon (CAF) is one of the lead-free era focused on board the theme, of course, a new generation of substrate must have better anti CAF ability, not only to a lead-free soldering in PinChu condition.
2.2, environmental protection laws and regulations
Environmental protection regulations for the substrate, in the political intervention has added a lot of additional requirements, such as the EU's RoHS and WEEE, and a number of directives, will affect the formulation of sheet specifications. In numerous regulations, RoHS limits the lead content in welding. Tin lead solder in the assembly plant has been for many years, the melting point of alloy is 183 DEG C, and the welding process temperature is about 220 degrees celsius. The mainstream of the lead-free solder tin silver copper alloy (such as the melting point of SAC305 is about 217 degrees Celsius, the peak temperature usually when welding will be as high as 245 degrees celsius. Welding temperature rise, represents the substrate must have better thermal stability to endure multiple welding caused by thermal shock.
The RoHS directive also disables some of the halogen containing flame retardant, including PBB and PBDE, etc.. However, PCB substrate in the most commonly used flame retardant of four TBBA two phenol, in fact, is not in the black list of RoHS. Nevertheless, due to containing TBBA plate in heating will produce inappropriate ashing reaction, resulting in some machine brands still consider changes to adopt halogen-free materials.
2.3, electrical requirements
High speed, broadband and wireless RF applications, force plate also has better electrical performance, i.e. dielectric constant DK and dissipation factor DF, not only must be suppressed and must be full board is stable, and should be properly prepared can be controlled. In accordance with these electrical requirements, but also had to be in the thermal stability of the inferior, the only way, its market demand and the share of the party to increase.