What is Manufacturing Process for Non-Plated Through-Hole PCBs

The Production of Double-sided PCBs with Printed through Holes

Usually, one-sided boards with non-plated holes are made, but sometimes it is necessary to make double-sided boards without plated through holes. Such boards can be obtained by aligning the pattern on both sides of the blanks.

In the course of the project of double-sided boards without plating holes, it is often necessary to install connections through them.

The easiest way in such cases is to solder the riveted hanging conductors to the contacts on opposite sides of the board. However, using component pins to establish connections is not recommended.

Alternatively, rivets are hollow copper rivets coated with solder or tin.

They are riveted to a funnel shape and soldered on both sides of the board. Or full riveting and melting on both sides is possible, but then it is necessary to cover the contact pads with solder.

One of the current methods is using thick polymer film (PTF) technologies.

For a long time, this technology was used for the production of high-temperature thick-film hybrid circuits, and only later it began to be used in the production of PCBs.

The purpose of using PTF technology is to obtain at a low-cost track, connections, resistances, and through printed holes in PCB bases.

The production of double-sided PCBs with printed through holes using PTF technology is most suitable for widespread PCB production, because during production, the operations of application, drying, and thermosetting of PTF paste are used.

PTF contains a conductive constituent consisting of silver particles, a polymer material, and a solvent, which provides the desired viscosity during application.

The silver paste is screen printed onto the copper layer of the board.

A vacuum acts on it, as a result of which the paste flows down the hole until 2/3 or 3/4 of the walls of the holes are covered, after which the board is dried.

After that, the board should be turned over. Silver paste is applied to the copper layer on the second side of the board and, as in the first case, it drains off under the influence of vacuum until it covers the first layer of the paste.

After drying and thermosetting, we get a through-printed hole, which ensures good electrical conductivity of the sides of the board.

It should be noted that such holes should not be used to install elements – only as vias since, in case of contact between the solder and silver during wave soldering, the silver will dissolve.

Note also that silver ions can move between two adjacent paths due to exposure to an electric field or moisture, which will lead to the occurrence of a leakage current, or even lead to a short circuit.

A protective layer in the form of a solder mask should prevent such problems.

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