Guidelines for PCB Prototypes Service

 
In the world of printed electronics, prototype PCB fabrication takes some time to master and manufacture. Apart from the process itself, there are a lot of considerations that a PCB prototype service needs to handle. Here are some of the design, assembly and fabrication (link article 26) guidelines that you must follow closely when a developing a PCB prototype.
 

1. Guidelines for Layout and Design

Component Selection

The section of components is an integral part of a fast PCB prototyping service and it usually demands using those components that are available readily. Just as soon as the BOM (bill of materials) is finalized, ordering the components must begin as the lead time may extend to more than 10 weeks after the order is placed. So, if you are availing or providing PCB prototype services for custom components, the lead time may stretch to more than a couple of weeks. Knowing which components are obsolete and which are available for the assembly is also extremely crucial.

Test Points

In the layout phase of a PCB prototype creation, it is essential that the ‘design for assembly (DFA)’ and ‘design for test (DFT)’ are evaluated carefully as a reckless calculation can result in an unfavorable time delay. Allocate test points at all the important modules of the circuit. It is preferred that you insert test points at just one side of the printed circuit board so that the use of dual test probes at both sides can be avoided.

Analog and Digital Plane Bifurcation

In a mixed signal circuit, separate test points should be inserted for analog and digital segments. Otherwise, noise from the analog part can disrupt the low power adjacent digital circuitry. Completely isolate the high frequency digital circuitry like the clock from analog circuits and shield the clock trace by placing a ground trace over it.

Coupling of High Speed Signals

In cases where the PCB prototype service is concerned with fabricating a 4 layer PCB prototype or making one which has a higher layer count, the high speed signal layers should be coupled to adjoining planes.

Routing for BGA and CSP

A PCB designer should ascertain that in the BGA and CSP routing, the signal lines do not run in parallel and line-to-line coupling is avoided in order to avoid glitches during logic transitions from one state to another.
 

2. Guidelines for Prototype PCB fabrication

Stackups and Impedances

In high speed circuits, stackups are of an important consideration for a fast PCB prototyping service. Stackups tend to create impedances in the circuit so targeted impedance must be calculated after the stackup layers are defined. The impedance calculations must be verified at the design phase and then later on at the prototype PCB fabrication step to assure that the signal is devoid of crosstalk.

Avoid Unnecessary Shapes and Unique Cutouts

In order to work towards a fast PCB prototyping service, it is essential not go for unnecessary board shapes and eccentric cutouts or else the manufacturing time would increase. Use standard shapes and cutouts in order to speed up the process.

Laser Drilling versus Mechanical Drilling

Laser drilling always consumes more time than the regular mechanical drilling so keep this in mind for prototype PCB fabrication.
 

3. Guidelines for Prototype PCB Assembly

Order before the Assembly Begins

In a fast PCB prototyping service, it is crucial that the stencils used for cutouts, fixtures and assembly are ordered at the time of the PCB fabrication process.

Assembly Inspection

Before the PCB prototype service enters the assembly stage, the inspection of the assembly packages should be completed. The surface mounted inspection programming could hinder the process and depending upon the complexity level of the PCB, this could take an additional 2 days. A key point to remember here is that ECAD programs must be used instead of a manual visual inspection. This is important to improve reliability and minimize time consumption.

Auditing the Kit

In order to expedite the process to ensure a fast PCB prototyping service during the prototype PCB assembly stage, it is important to ascertain all the desired components which are ready for assembly. At least the surface mounted components should be ready if the PCB has a small percentage of thru-hole components. Surface mounted components can be fixed beforehand and the thru-hole assembly can be soldered later on.