日本語
PC Board materials Materials Choosing the Right One for the Application
655
0
Nov 20.2013, 16:22:00
PC Board materials are available in various grades, as defined by the National Electrical Manufacturers Association (NEMA). It would be very convenient for designers if this organization was closely allied with the electronics industrycontrolling parameters such as resistivity and dielectric constant of the material. Unfortunately, that is not the case. NEMA is an electrical safety organization, and the different PCB grades primarily describe the flammability, high temperature stability, and moisture absorption of the board. Therefore, specifying a given NEMA grade does not guarantee electrical parameters of the material. If this becomes critical for an application, consult the manufacturer of the raw board stock. Laminated materials are designated with FR (flame resistant) and G grades. FRC1 is the least flame resistant, and FRC5 is the most.
Do not use FRC1. There are many examples of boards with burned spots, where high wattage components have heated a section of the board for a period of time. This gradeof PCB material has more in common with cardboard than anything else. FRC4 is commonly used in industrial-quality equipment, while FRC2 is used in high-vol-ume consumer applications. These two board materials appear to be industry standards. Deviating from these standards can limit the number of raw board material suppliers and PCB houses that can fabricate the board because their tooling is already set up for these materials. Nevertheless, there are applications in which one of the other grades may make sense. For very high frequency applications, it may even be necessary to consider Teflon or even ceramic board substrate. One thing can be counted on, however: the more exotic the board substrate, the more expensive it will be.
In selecting a board material, pay careful attention to the moisture absorption. Just about every desirable performance characteristic of the board will be negatively impacted by moisture. This includes surface resistance of the board, dielectric leakage, high-voltage breakdown and arcing, and mechanical stability. Also, pay attention to the operating tem-perature. High operating temperatures can occur in unexpected places, such as in prox-imity to large digital ICs that are switching at high speeds. Be aware that heat rises, so if one of those 500-pin monster ICs is located directly under a sensitive analog circuit, both the PCB and circuit characteristics may vary with the temperature. After the board substrate material has been selected, the next decision is how thick to make the copper foil laminated to it. For most applications, 1-ounce copper is sufficient. If the circuit consumes a lot of power, 2-ounce may be better. Avoid ½-ounce copper, be-cause it tends to break between the trace and the pad.
Prev: Single-Sided PCBs
Next：Prototype of the PCBs
- Comments(0)
Upload a photo:You can only upload 1 files in total. Each file cannot exceed 2MB.Supports JPG, JPEG, GIF, PNG, BMP
