Tips Information on how to “” Optimize “” Printed Circuit Board Layout

To provide useful suggestions, we want to inform you about some “” simple rules “” to keep in mind to “” optimize “” the printed circuit board layout for “assembly and testing. When followed, this information”“plays”“a key role in” board assembly!
Both SMT and PTH (axial and/or radial) component assembly machines, solder paste deposition systems, and testing machines always require at least 2 reference points (fiducial marks) usually positioned near the board corners – it’s important to include these.
These fiducials can consist of two exposed copper dots with a 1.5 mm diameter without solder mask. (Fiducial marks can have various shapes: Squares, diamonds, circles, etc).
The dimensions of printed circuit boards usually should not fall below a minimum threshold (for example, we can consider 50 mm x 50 mm). In such cases, it’s advisable to use a panel* with multiple units along both “X and” Y axes (* see the specification on the website or request it from our This email address is protected from spam bots. Enable Javascript to view it. “technical office ).
Regarding maximum dimensions, typically, it’s best not to exceed 400 mm in X and 250 mm in Y.
Prime Srl, with its “specialization in certain applications, can assemble boards of”“significant”“dimensions, up to 645 mm in X and 400 mm in Y.
Consider that boards and/or panels move through” machines using guide rails: therefore, it’s important to have at least 4/5 mm clearance from components in these areas. If this isn’t possible (components too close to the edge), a rail strip must be provided. (Often by properly optimizing the panel layout, you can avoid adding rail strips to the board, saving costs – consult our This email address is protected from spam bots. Enable Javascript to view it. “technical office ).
When possible, keep SMT components for modules that can only be soldered once, and PTH on one side.
If this isn’t possible, place active SMT components and PTH on one side and passive SMT components on “the other; this will still allow wave soldering of the board.
In this regard, it’s important to properly size the pads on the passive side and ensure all components are in the same direction, being careful to avoid” shadow areas. (Consult our This email address is protected from spam bots. Enable Javascript to view it. “technical office ).
Avoid vias passing through pads (place the via next to the pad): this also acts as an escape route for solder paste.
Ensure access to all areas of the board where manual soldering and/or rework may be required.

We would now like to present some “” suggestions “” to ensure that the board can be easily “” tested “” by flying probe systems.
Our test system consists of 4 independent flying probes capable of performing in-circuit, functional, and visual testing on any type of electronic board.
For accurate data measurement, the machine’s probes (needles) need proper contact with the board’s test points.
The following are simple guidelines that, when considered during PCB development, provide valuable support for automatic testing in terms of reliability, without increasing costs.
To achieve good test coverage of the board, ensure that every single circuit polygon to be tested is accessible by the flying probes. For this purpose, position test points on the same side when possible (which will be the testing side).

Test point characteristics:
The best contact points for flying probes are:
– test pads free from solder resist, via holes, through-hole component leads (PTH), SMD component pads.
– the minimum test point size is “7 mils (12 mils recommended), with a spacing of 16 mils between points (20 mils recommended).
– Via holes must have a minimum diameter of 12 mils (16 mils recommended), must always be occluded and not covered by solder resist.
– If testing with mobile capacitive probe is planned, position all integrated circuits on the same side if possible.
– Position any mechanical components (heat sinks, supports) so they don’t prevent “the possible placement of fixed probes on the opposite side to the test side. (For example, if we want to bring two power supplies to a specific area using two fixed probes)
– For SMD components, especially those with pitch less than 25 mils, make the solder pad slightly longer than the component pin so that the test equipment’s probe can contact the test point on the solder pad itself rather than on the” pin.
– When creating the board’s electrical schematic, include signal names even for unconnected component pins to enable testing.
– If the CAD allows, assign a test channel number to each polygon during board development.
– Provide two signal names on the same polygon when dealing with resistors less than 100 ohms.

If board power-up testing is planned:
I. The best way to connect the board’s power and ground points to the system’s power supplies is through a connector. If the board design doesn’t include this solution, two pads on the opposite side to the test side are used, which must have the characteristics described below.
II. Power and ground pads must be sufficiently large (min. 2 x 2 mm) to allow easy positioning of fixed power points. They must also be at least 4 cm apart to accommodate magnetic retention test probes with a 2 cm diameter metal base.
III. Always assign the same channel numbers to power and ground points, even on different boards, to quickly identify these points (especially during program debugging).
Capacitors
Don’t assign the same component name to electrolytic and ceramic capacitors. Having two different names allows associating two different test macros during test program development.