Print — from design to finished circuit

When a circuit diagram is drawn finished, there's still a long way to a working device. The diagram shows how components should be electrically connected—but a printed circuit board (PCB) must also solve the physical task: to hold components in place, connect them precisely, and do it cheaply and reliably to manufacture in large quantities.

§From layout to layers of copper

The print is built up of an insulating base material with thin layers of copper pressed on. The copper is etched away where it should not be, so what remains forms the tracks the current should run in — the circuit's 'wires'. Simple prints have copper on one or two sides, while advanced electronics often use multilayer boards with several layers of copper inside the board, connected through small plated holes (via). The denser and more complex the circuit, the more layers are typically required to fit all the connections without them crossing incorrectly.

§Through-hole mounted or surface mounted?

Components can be assembled in two basic ways. With through-hole mounting (THT) the component's leads are inserted through holes in the board and soldered on the underside — this provides a mechanically strong connection, suitable for components exposed to pulling or impact. With surface mounting (SMT/SMD) the component sits on top of the board and is soldered directly to pads on the surface, without holes. SMD components are far smaller, can be placed closer together, and today dominate most modern electronics, while THT is still used for connectors, larger components and parts that must withstand mechanical stress.

§From machine to finished circuit

In production, components are rarely assembled by hand. A pick-and-place machine places SMD components with great precision, after which the board is sent through a reflow oven, which heats it evenly so the solder paste, which is already printed on the surfaces, melts and forms the connection. THT components are often soldered instead by wave soldering, where the board is carried over a wave of molten solder. In workshop and development, however, you still solder by hand with iron, tin and a steady hand — the technique you practice yourself when you learn the trade.

§The IPC standard – when is an assembly good enough?

For quality not to be a matter of taste, there is an internationally recognised standard for electronics production: IPC-A-610 which describes how to visually assess solder joints, component assembly and the general condition of the board. The standard operates with three classes where class 1 covers common consumer products, class 2 covers equipment that must work reliably over time and class 3 covers equipment where failure can be critical for example in medical or other high-security electronics. A defect that is acceptable in class 1 can be unacceptable in class 3.

• 01Acceptable — the joint meets minimum requirements and is approved
• 02Process indicator — does not affect function now, but points to something that should be improved in the process
• 03Defect — the joint does not meet requirements for form, fit or function, and must be reworked

§Why it concerns you as an electrician

Regardless of whether you work at the bank or at the mortgage institution, your task is to place the loan in the customer's overall finances. You must be able to explain the connection between loan limit, contribution rate and term, and you must calculate what the total payment means for the customer's disposable income — not only today but also if interest rates rise. Many banks and mortgage institutions work closely together or are part of the same group, so good housing advice often combines a bank loan and a mortgage loan in one overall plan.

“A print is a plan that has become copper — and the standard is the common measure of whether the plan is carried out properly into life.”

— Professional view on print production.