wisepowder: Goodbye, FR-4, we’re going to miss you

wisepowder

Goodbye, FR-4, we’re going to miss you


In the world of printed circuit boards (PCBs or PC boards), FR-4 has been the “go to” substrate for decades. (There was an industry attempt to call them printed wiring boards—PW boards or PWBs—that that just never caught on.) This fire-resistant material (hence the “FR” designation) is composed of a matt of fiberglass and epoxy, is usually green in color (Figure 1), and is available in many versions to suit the diverse needs of the design objectives.To get more news about fr4 circuit board, you can visit pcbmake official website.

As the literal and figurative foundation of so many electronic products, PC boards have industry standards and standards-setting organizations such as NEMA and IPC, a global trade association for the printed-board and electronics-assembly industries, their customers and suppliers. Interestingly, IPC was founded in 1957 as the Institute for Printed Circuits, then changed the name to Institute for Interconnecting and Packaging Electronic Circuits, and then changed it to the more-anonymous IPC. (This is similar to the action of the Institute for Electrical and Electronic Engineering, which legally changed its name to “IEEE” and IBM which is the corporate name and not a nickname for what was previously known as International Business Machines.)

I won’t go into the details of FR-4 and its defining standards, as there are good online sources (including at Wikipedia [Refs. 1-3]). Due to the wide use of this substrate, it is available in standard thickness of 0.031 in (0.78 mm ), 0.062 in (1.57 mm) and 0.093 in (2.36 mm). The copper cladding can be on side only side or both sides, and the standard thickness of laminated cladding of lamination is usually 1 ounce copper/square foot of board or 35 µm (called “1 ounce” in the US); two and three-ounce is also in use as well as the thinner half-ounce laminate. Some PC boards do not use pre-clad boards but instead use an additive copper process, where copper is deposited where needed rather than chemical- or laser-etched away where it is not needed; each approach has electrical, cost, trace density/thickness, and other tradeoffs.

In many designs, multiple PCB layers are stacked to support ever-more complex and dense interconnects, and there are boards with 20 or more layers. Two sided and multilayer boards have plated-through holes connecting the various layers to provide both electrical and thermal conductivity. These vias (formal name is “vertical interconnect access&rdquo have their own variations: they can be through hole, buried, or blind. The latter connects internal layers only and are a troubleshooting and repair nightmare.
FR-4 material is rugged, has fairly good electrical and mechanical specifications, and those numbers are reasonably stable over time and temperature. It does, however, dull and wear drill bits and cutting shears quickly, because it is fairly hard and abrasive (and the glass splinters you get from handling the edges are brutal).

In the days of through-hole components, before surface-mount technology (SMT) ICs took over the PC board world, a typical board could have hundreds of holes, so this was a significant consideration; fabricated PC boards were often priced primarily by their size and number of holes. The near-universal use of SMT devices has greatly reduced the number of holes needed to a just few as needed for mounting screws, larger components, some connectors, and other unique attachments.
Many engineers improvise small, custom enclosures of cladded FR-4, soldering the seams from one end to the other for full shielding of an entire circuit or a sub-circuit; the late Jim Williams and Bob Pease both show this technique in many of their prototypes. It’s uses go beyond electronics: I once cut two U-shaped pieces of FR-4 and sewed them as stiffeners into the handles of a family heirloom leather briefcase, Figure 2; I don’t want to do that again, ever!