Computer Aided Manufacturing or ‘CAM’ Engineering is the most critical part of printed circuit board manufacturing as this is where design criteria’s are measured and checked to ensure the designed is able to be manufactured.

Some of the basic checks include:

·      Track width and clearance is appropriate for the copper thickness requirement

·      Solder mask bridges between IC’s have sufficient space

·      Sufficient annular ring for all plated holes

·      Minimum hole-to-hole clearance

·      Minimum hole-to-pad clearance

·      Minimum hole- to-track clearance

·      Sufficient inner layer clearances

·      Minimum silkscreen height

·      Minimum silkscreen lines

·      Ensure no exposed copper after solder mask (except the pads and SMT components)

·      Where vias are to be tented (covered) with solder mask, adjust the solder mask file accordingly

·      Multi-layer stack-up sequence

CAM engineering will then set up the required file packages which can be downloaded at each stage of production as required:

·      Photo-plotting all films for copper layer primary image, photo-printing primary image, solder mask, component legend silk-screen

·      CNC drill files – initial plated through hole drilling files

·      CNC route files – profiling, internal and external notches and cut outs

·      CNC non-plated drill file - there may be further non plated holes to be drilled

·      CNC v-grooving files – v-cut or v-grooving these days is predominantly processed with CNC v-grooving machines

·      Net list probe test/ jig test files for bare board electrical testing

·      A job card/traveller will be generated listing all the required finishes on the printed circuit board order for each stage of fabrication which include the following:

o   Customer Name

o   Part Number / Revision

o   Layer count

o   Stack up sequence
Material type

o   Finished Thickness

o   Copper thickness

o   Unit size

o   Finished panel size if panellised

o   Production panel size

o   Surface finish

o   Solder mask colour

o   Silkscreen component legend colour

o   Special instructions

Fabrication packages are created which are used in various workflow production stages including films for drilling templates/checks and fabrications drawings for final QA which list all the finished requirements with tolerances depending on the fabrication requirement; Class 2, Class 3, Mil Spec, etc.

CAM Engineering will receive the customers Gerber files which may or may not be panellised. For this example, we can assume that the PCB Gerber files were supplied as a single unit. We would then proceed to panellise these to ensure productivity through SMT assembly by adding top & bottom tooling strips with tooling holes and fiducial marks. The example below is panellised 4 up (2x2) with 10mm top & bottom tooling strips with 4 x 3.0mm tooling holes and 3 x fiducial marks with solder mask clearance.

PCB Global’s CAM engineering is always processed and updated with the customer’s permission and authorisation to ensure the highest quality PCB Gerber files are provided to allow for minimum EQ’s, ensuring the fastest possible lead time for all of our customers. For further tips and information when designing and laying out your printed circuit board design file please do not hesitate to contact our PCB Global team at sales@pcbglobal.com

Printed Circuit Board Panel - Top & Bottom tooling strips

PCB Global can apply our standard top & bottom tooling strip when requested to panelize a customer’s single image printed circuit board file as detailed below;

TOP TOOL STRIP

BOTTOM TOOL STRIP

Fiducial Mark Specification:

Clearance area between circle and rectangular is 3 mm or more.

7.5 x 7.5 mm square                                               

Electronic Questions, or EQ’s are common for many queries concerning silkscreen on pads. PCB Global’s Computer Aided manufacturing (CAM) Engineering department will always be ready to answer and confirm with customers whenever a question arises.

Silkscreen on Pads

EQ from CAM:

Silkscreen component legends on the plated holes or vias.

Explanation:

It is not common to have any silkscreen component legend on any copper area whatsoever. This results in a poor quality printed silkscreen legend which can be illegible to your design and use of PCB’s. In some cases, the PCB designer has no choice but to apply the component legend silkscreen as per the below image as there is no room to move these designators (see below).

 Resolution:

With validation from our customer, the silkscreen component legend was printed as per the file resulting in some incomplete text in areas.

For further tips and information when designing and laying out your printed circuit board design file please do not hesitate to contact our PCB Global team at sales@pcbglobal.com

EQ’s for a variety of printed circuit board design files are common to PCB Global’s Computer Aided manufacturing (CAM) Engineering department. We will invariably have a few Engineering Questions to confirm with our customers, such as the example shown below regarding Solder Mask Bridges.

Solder Mask Bridges

EQ from CAM:

These SMT pads do not have enough space between them to apply a correct solder mask dam. This area will be completely free of solder mask, or can be shaved by 2mil from each SMT pad then apply the solder mask between each section.

Explanation:

Currently this SMT area has the solder mask open as one block. This is an acceptable clearance; however, it can cause shorts between these pads after SMT reflow. By shaving 2mil from each SMT pad, we can ensure there is sufficient distance to allow for exposure of the solder mask file, to apply solder mask between each SMT pad. This ensures the solder mask dam will improve the solder reliability yield after SMT reflow.

The actual distance between SMT pads differs depending on the finished copper thickness/ Below is an example of 1/2/3 & 4oz copper finish:

Solder mask bridge for 1oz copper (4mil)

Solder mask bridge for 2oz copper (5mil)

Solder mask bridge for 3oz copper (6mil)

Solder mask bridge for 4oz copper (6mil)

 Resolution:

With authorisation from our customer, the SMT pads in question had the copper area shaved 2mil allowing a solder mask dam between these IC’s.

For further tips and information when designing and laying out your printed circuit board design file please do not hesitate to contact our PCB Global team at sales@pcbglobal.com

Engineering Questions or EQ’s are very common with new printed circuit board files and designs. PCB Global’s Computer Aided manufacturing (CAM) Engineering department will invariably have a few EQ’s depending on the quality and consistency of the files provided. One example of a typical EQ regarding Hole to Track clearance is shown below:

Hole to Track Clearance

EQ from CAM:

This non plated through hole (highlighted in green) is only 5mil from the track. The absolute minimum distance is 6mil.

Explanation:

Non plated through holes are drilled at the final stage during CNC routing. The close proximity of these holes shown in the file are too close as the copper tracks and copper pads may place stress on the copper area during the CNC non plated drilling process, resulting in a weak point.

Resolution:

With approval from our customer, the track to non-plated through hole violation was resolved by amending the track travel (highlighted in red) which resulted in a 12mil clearance.

For further tips and information when designing and laying out your printed circuit board design file please do not hesitate to contact our PCB Global team at sales@pcbglobal.com