The basics of FR-4 Printed Circuit Boards
Posted by freemexy on January 5th, 2021
Part 1 of this FAQ provided context and background on the PC board, and discussed its first widespread appearance as a phenolic-based board. Part 2 looks at some board issues and the widely used FR-4 PC board substrate.To get more news about fr4 board, you can visit pcbmake official website.
Q: I see the term “solder mask” — what is that?
A: Solder mask (also called a solder stop mask or solder resist) is a thin, lacquer-like layer of polymer that is usually applied to the copper traces of a printed circuit board (PCB) for protection against oxidation and to prevent solder bridges from forming between closely spaced solder pads. It is not applied to the places where component leads and PC board traces meet and must be soldered in the soldering wave machine or soldering oven.
Q: How are designations (callouts) such as IC1 or R4 printed onto the PC board?
A: After the solder mask is applied, a silkscreen with the needed designations is printed onto the mask. Green is the most common color for the silkscreen, but other colors are used.
Q: I don’t see many of these phenolic bards, so what happened?
A: They simply could not handle the requirements of electronics circuits and components into the 1980s and 1990 in terms of thermal and mechanical stability, consistency, ability to support narrow traces and tiny holes, and two-sided and multilayer demands. Thus, the glass-epoxy PC board was developed; the most-common version is known as FR-4 (sometimes written FR4
Q: Can you tell me more about FR-4?
A: FR-4 is a general designation for a matrix of fiberglass and epoxy which is used for most of today; s PC board substrates. It is available in various standard thickness, chosen as a function of the size of the board, flexing issues, and rigidity requirements. ). The FR-4 designation is now also a generic term used by many engineers for any fiberglass-epoxy PC board, even if it is not FR-4 in the formal standards sense, as there are many substrates which are similar to FR-4 but do not adhere to the formal specification.
Standard single-weight thickness is 0.031 in (0.78 mm), followed by double- and triple-thicknesses of 0.062 in (1.57 mm) and 0.093 in (2.36 mm), respectively; thinner ones are also available. Reference 1 has a table listing about 30 of the nominal electrical and mechanical characteristics of FR-4; they are vital to consistent performance and the ability to use different sources for raw boards and fabrication. FR-4 usually green in color, but other such as blue are sometimes used. There is no standard PC length or width, nor does the board have to be rectangular; it can be circular and have cutouts or whatever is needed. In many ways, the green PC board is the defining image of modern electronic circuits (Figure 1).
