Fast PCB prototype

In order to understand what there can be time savings in the prototyping line, it’s necessary to understand how long it normally takes to get a prototype or First Article as they are known in the industry.

So let’s see if we can recap what we have said so far: the PCB process start with a basic product definition, no more that a sketch and a block diagram showing the basic components and some ideas on how they can be outlined. Detailed engineering shows that there is a need for a number of layers, provides an idea to the designer of what components need to routed out and what are the basic connections.

From this detailed engineering the designer completes a regular design. Regularly it will depend on the complexity of the design how long does this take. It could be very short if there aren’t many components, but then again most of the time the design requires a certain degree of complexity with multilayer designs including a good number of independent components. This being the case, an approximation is that it takes a week to complete each layer.

Now follows the interaction with the PCB manufacturer. Here assuming the design house and the designer are two separate entities, this process is very rigid and structured in such a way that all parties can provide their inputs accordingly. The manufacturer usually is only contacted when the design is complete, although the designer could potentially be sending partial updates to them as she progresses in the project, yet this hardly ever happens. The reasons are multiple: lack of resources on the manufacturer site to be checking partial projects, preference to evaluate once the design against capabilities, more accurate quoting, etc.

PCB pro quick cycle

ROHS comliant fast boards

So once the design is completed the manufacturer provides input to the design and sends it back. The designer can choose to ignore or incorporate those suggestions and the process starts again. This step could take several weeks, again depending on the complexity of the design. Normally a week takes for the PCB maker and the designer to agree on the final design.

Once this latest step is complete, manufacturing starts: usually the first step is to take the design Gerber files and use an assembler to transfer those into glass masks which will be used in the exposing process. With the masks complete the following steps are to align mask to substrate, exposing this assembly to UV or visible light depending on the type of photoresin used and developing using solvents to remove the unreacted portion of the resin. This leaves a pattern that should resemble the original design, including vias, traces and other areas where metal has to go.

The next step is cleaning and metallization. There are several methods used commercially to grow copper films: electrolytic deposition, electroless deposition, CVD and sputtering. By far, the PCB industry has gone with the first one. In this method a solution cotaining a copper salt is used as an electrolyte, the board is used as one electrode and current is circulated between that and a second normally pure copper bar, acting as the second electrode. This process causes the Cu ions in solution to deposit as metallic copper on the surface of the activated substrate, thus growing films of specified thicknesses. The thicker the film the longer it takes to plate copper and more costly it becomes.

After metallization, a film of glass fiber reinforced epoxy is laminated on top of the metal, it is used as the insulator layer that separates one metal layer from the next. In this way layer after layer of material are formed. The estimated time to have a complete prototype from the initial reception of the design until the moment is ready for shipment is again one week per layer.

As can be deducted from the previous discussion there is a great deal of intermediate steps. And because of that, creative designers and manufactures have devised shortcuts to fasten the process along to get can provide aggressive timelines to deliver FAs to their customers. Some examples of those are:

- Increasing the metal density with aggressive design rules, thus saving space and decreasing the number of layers.
- Faster glass fabrication
- Faster rate Cu plating solutions
- Additional capacity to laminate and trim
- Faster shipping

One thing that has to be kept in mind is that these changes might result in quality compromises; so careful attention should be given to the design check stage to make sure that bugs are captured before they crept out into the production stages.

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