Production organisation information for the manufacture of printed circuit boards (PCBs)

During our work, we are often tasked by our partners with assignments related to the production and mounting of printed circuit boards. In our next post, we wish to offer them help with some practical guidelines that would make common work more efficient and faster.

Two fundamental situations may arise upon planning and production.

In the majority of cases, we produce boards we have designed, but it often happens that our clients contact us with their own PCB production and mounting needs.

To solve the latter task more smoothly, it is worth noting some technical information. According to our experience, only the observance of these aspects allows optimal production organisation, resulting in the best implementation time for our clients.

As our company doesn’t own production lines, we use the help of subcontractors for the production processes. Relying on its many years of experience, ProDSP knows precisely what companies are the best to cooperate with in this field.

Let’s see what data we’ll need from our clients before production begins:

For the production of PCBs, we need the Gerber files and the drill files for every layer to manufacture.

What we need by all means in this category:

Copper layers (top-bottom layer and any occasional internal layers)
Soldering mask layers (top and bottom side)
The layer containing the perimeter of the board
Drill files of metallised and non-metallised holes (.txt extension)

The following files are optional:

Paste layers (from the side where there are components are mount)
Inscription layers for screen printing (from the side the screen inscriptions are required)

In addition to the production files, determining the following technological characteristics is also necessary for the production of PCBs:

Board thickness (1.55 mm by default, requests for different thicknesses must be indicated)
Layer structure (thickness of copper foils on the external and internal layers)
In case of impedance-matched signals, the entire layer structure by providing the thicknesses of the insulation layers
Finishing material (by default, any surface treatment procedure is lead-free, but selective gold coating may also be requested, which is recommended integrated circuits (ICs) with small pin-to-pin pitches, and obligatory for ball grid array (BGA) ICs.
Colour of lacquer layers (green by default, alternative colour requirements must be indicated)
The glass transition temperature (Tg) of the PCB material (material by default: 145-150 °C, higher Tg requirements must be indicated)

How to continue after the preparatory phase?

As the next step of the process, we select the appropriate PCB producing company based on the above files and data.

To prepare a quotation, we also need to know the number of boards to produce (clearly indicating for panelised boards whether the quantity applies to boards or panels) as well as the expected deadline.

As a partner providing full service packages, following the PCB production, we are more than happy to organise mounting of the boards, including the procurement of the components.

The manufacturing of PCBs and the procurement of components take place simultaneously in an optimal case, meaning that we need the bill of materials (BOM) containing the list of components for the board at the time the PCB production files are provided. The BOM must contain all materials that must be required for mounting.

If our client provides components for production, it must clearly indicate who is responsible for the procurement of which component: our client/ProDSP.

The format of BOM is tabular, which must include the following columns:

The exact MPN (Manufacturer’s part number) of the component
Quantity
In case of standard passive components, it is a value, and other parameters - if the MPN is not available, then this is absolutely necessary, otherwise optional.
Designator – (not required for procurement but necessary for mounting)

The other information are not absolutely necessary, but it is a great help if the customer provides them:

Distributor
Distributor’s article number
Housing

In the next phase of work, we check the actual availability of the components, knowing the above information.

In reconciliation with our customers, we replace problematic items with available substitute products. (The current global chip shortage may occasionally necessitate compromise solutions).

Following procurement of the empty PCBs and components, all raw materials are available for mounting, which depends on the complexity of the board, the number of components and the number of boards to assemble with manual or mechanised mounting.

Determining this is not our task, but it depends on the mounting method what other files we need.

For manual mounting, the following files are required:

BOM designator with information
A well legible and searchable mounting drawing, separately for the top and bottom sides, in PDF format

For mechanised mounting, the following files are required:

BOM designator with information
Gerber files, based on what has been introduced in the PCB manufacturing chapter
Pick and Place file (in .txt/.csv format) with the following columns
Designator (component identifier)
Side information (top/bottom)
Housing
Center X (component position’s X coordinate)
Center Y (component position’s Y coordinate)
Rotation (angle of angular displacement)

It helps the work of the mounter if a 3D drawing is available of the circuit, as this can often clarify determining the correct orientation of the connectors.

It is important to note that if questions or lack of components should emerge mounting, reaction is required within a short deadline, otherwise the components may be unloaded from the machine.

In these cases, the quick reaction of our customers may be necessary, if only they are able to answer the emerging questions substantially. Reloading the component may incur unexpected costs and deadline postponement, which are unpleasant for all parties concerned.

The smooth reconciliation of the technical details, the complete documentation and quick and efficient communication are the key to successful cooperation in every project of this type.

If you should have questions concerning any detail of the process, feel free to turn to us, we’ll help!

Author:
Eszter Tóth, senior hardware designer