Lamination is the process of stacking and pressing layers of copper foil, glass fiber prepreg, and the inner layer of a circuit board to produce a multi-layer PCB. This is one of the key processes in multi-layer PCB manufacturing. High heat and pressure are applied in the process to soften the prepreg to make it adhesive. After lamination, an automatic X-ray target hole drilling machine is used to drill guide holes in the circuit board, which helps align the internal and external circuits. The edges of the boards are then trimmed to facilitate subsequent processing.

A drilling machine is used to create through-holes in each circuit layer and holes for components to be soldered into. When drilling, pins are used to fix boards to the machine work table through the previously drilled guide holes. A back-up board (phenolic resin board or wood fiberboard) and an entry board (aluminium foil) are also used to minimize burrs. We would reduce the number of layers when the customer’s design requires holes of higher precision.

The circuit board is immersed in a copper solution, and with the help of an electric current and a metal catalyst, the copper ions in the solution are reduced and precipitate on the through-hole wall. This is how a circuit with through-holes is formed.

Using copper sulphate plating method, the inside of through-holes is plated with copper that is thick enough to resist subsequent processing and environmental impacts.

Blind Hole：starts from the surface layer of the PCB and extends down to one or more internal layers;

Buried Hole：connects inner layers of a PCB. After lamination, buried hole cannot be seen from the top or bottom of the PCB, which means they don't occupy space on the outer layer.

Processes: Abrasion ⇨ Laminating ⇨ Holding ⇨ Exposure ⇨ Holding ⇨ Developing

Dry-film: photo-resist is used;

Exposure: exposure machines use parallel light (vertical light source, line width / line space of 3/3 mil) or scattered light (less precise; can be used when line width / line space is larger, about 8 mil or more);

Developing: remove parts of the dry film unexposed to the UV light with a developer solution. The remaining dry film is the intended circuit.

Pattern Plating: this is a positive film process. An initial copper layer is applied to achieve the required thickness. A layer of tin is then deposited over to protect the copper layer from etching.

The etching process for positive films involves the processes of stripping , etching and tin-lead stripping to achieve the required circuits. For negative films, etching can be done directly after developing without pattern plating.

After the outer circuit is completed, a layer of LPSM is applied to prevent exposed copper surfaces from oxidizing oxidizing and short circuits between solder pads and component leads.

The customer’s desired legend, logo, or component symbol with number is printed on the board using screen printing. After printing, the ink is cured through baking or UV light exposure.

Ink color for legends usually come in black, white and yellow;

Types of legend inks: Post Cure (PC), Ultraviolet Cure (UV).

A tin layer is sprayed onto the soldered pads of a board, which is then covered with a layer of solder alloy through hot air leveling for protection and solderability. (Liang Dar currently provides tin-silver-copper and copper-nickel-tin.

ENIG means electroless nickel / immersion gold. No electrical current is applied during nickel deposition. The nickel-phosphorus alloy layer can be continuously deposited on the activated metal surface using a reducing agent (such as sodium dihydrogen hypophosphite) in the high-temperature bath solution.

Punching: circuit boards are cut to the customer’s desired size using a punching machine. The pros of using a punching machine are efficiency and dimension precision, while the cons are costly toolings and potential burrs on the edges.

NC Routing: the circuit boards are cut to the customer’s required dimensions using a CNC routing machine. When cutting, the circuit boards are fixed to the CNC routing machine with pins inserted into the guide holes drilled prior. The pros of CNC routing include smooth board edges, minimal burr formation, and a cleaner process with less waste. The cons are slower processing speeds, higher total costs compared to the punching method, and potential challenges in achieving precision tolerances.

It is usually necessary to create break-away on panelized circuit boards to help the customers split or de-panel later on;

After the first article is manufactured and before proceeding with mass production, the residual PCB thickness is measured using a V-CUT residual thickness gauge that can provide printable data.

100% testing PCBs with high and low voltages, short/open circuit detection tools and flying probe testers to determine whether there are any short circuit/open circuit issues and to check the connectivity of the plated through holes. However, these methods are limited to assessing the connecting parts of the PCB. To detect other circuit defects, additional methods are required.

After open and short circuit testing, workers will carefully inspect the PCB appearance to ensure product quality.

Before packaging, a final impedance test, solderability test, and thermal shock test are conducted. Afterwards, PCBs are baked moderately to eliminate moisture absorbed and relieve thermal stress built up in the process. Lastly, the PCBs are packaged and ready to be shipped out.