Circuit Board Return Path Via Placement Options

Introduction
This blog discusses a few options that new circuit board designers may use for return path vias as a result of signal traces changing circuit board layers through using vias.
 
Further Literature
It is highly recommended that existing content from industry figures such as Eric Bogatin or Rick Hartley are reviewed. Related circuit board information is available from YouTuber channels such as Robert Feranec or Phils Lab to mention a few.

PCB Routing Example
For circuit board designs that feature microcontrollers, microprocessors, FPGA or similar devices with high pin count or spacing density the existing connections to power rails through vias can serve as return paths. In the image below, taken from the Altium Mini-PC board, the green highlighted vias indicate the several 0V (GND) power connections that may function as return paths for the DDR memory address, data, clock and control signals.

Altium Mini-PC Board Highlighted GND (0V) Vias (Courtesy Altium)

 
Reducing Return Path Distance
The capture below is a further extract from the Mini-PC demonstration board showing a distance measurement between a return via and a differential DDR clock pair.

A Texas Instruments Application Note, High-Speed Interface Layout Guidelines, 2023 states that the signal to return via distance should be a maximum distance of 5 mm (200 mil) although that value could be considered design dependent. For the Mini-PC demonstration board, the distance between the return via and differential pair is small, some 2.1 mm.

Altium Mini-PC Board Differential Via Pair (Courtesy Altium)

Consider a situation where the return path distances needed to be reduced. On the Mini-PC board, a smaller distance could be achieved following a circuit board review. Traces on the layers could be moved to make room for a via closer to the differential via pair. The capture below shows one possible change with a reduction to 1.4 mm.

Altium Mini-PC Board with Closer Return Path Via (Courtesy Altium)

Board Space Limitations
A more common limitation when adding or altering return path vias could be related to circuit board space. In the example below, the traces in the red colour identify a differential pair. There is no return path via in close proximity. The while highlighted rectangles represent pads on the other side of the circuit board.

Differential Pair with No Return Path Via on a Double Sided Circuit Board

The reason for no return path via in the area is two-fold. On the opposite side of the circuit board is a surface mount component with large pads making return via placement difficult. The second limitation is due to the PCB rules. The smallest via hole size is configured for 0.3 mm.

The limitation created by the component on the opposite side can be overcome using a number of solutions. Using the existing circuit board via the size of 0.3/0.5 mm (via hole size/via diameter) three vias could be placed onto the circuit board as shown below. This solution yields a differential pair to return path via distance of 2.3 mm.

Differential Pair with Three Return Path Vias on a Double Sided Circuit Board

Differential Pair with Three Return Path Vias on Other Side of Circuit Board

Another solution to consider is changing the board design rules. The circuit board clearance rule could be reduced from 0.2 mm to 0.15 mm since the smaller clearance is supported by many fabrication houses. 

Paired with the board clearance change, the via hole size could be reduced. For instance, a via of hole size and diameter 0.254/0.444 mm could be selected. In regards to capabilities, circuit board fabrication houses can manufacture smaller via hole/diameter measurement of 0.15/0.28 mm (drilled). Applying the two changes mentioned in this section, a via can then be placed less than 1 mm from the differential pair.

Differential Pair with Single Smaller Return Path Via on a Double Sided Circuit Board

No Space or Other Limitations
For some board designs, it may be impractical to place a via close to a signal that requires a return path. Should board space and routing permit, via stitching throughout the board or a via shielding around the board or relevant section of the circuit may be alternative solutions.

Example of Via Stitching on a Circuit Board

Example of Via Shielding on a Circuit Board

Summary
Even though the placement of return path vias may be a semi-automated process with some software design tools, the lack of circuit board space to position vias in optimum locations still vexes novice and experienced board designers alike. This blog puts that other solutions may be found by reviewing the nominated fabrication house’s manufacturing capabilities and the minimum manufacturing circuit board requirements.

Salvaging from LG Controller Board EBR369328

Introduction
This microblog reviews the electronic components (parts) that could be salvaged from an LG air conditioner compressor inverter controller board.

LG Control Board EBR369328 Top Side

Summary
After being provided with the inverter controller board for spare parts, it seems relevant to detail salvageable electronic components in this blog.

Being unfamiliar with air conditioning (AC) equipment, AliExpress was used to identify the function which is listed as an LG three-phase inverter compressor (motor) control board.

It should be noted that the LG control board was supplied not working. In these instances when salvaging electronic parts, additional testing and diligence should be taken.

Salvageable Top Side Components
For the current measurement on the three-phase supply, an Allegro device capable of + 50 A, part number ACS756 was utilised. The Allegro part is listed as obsolete however this does not prevent is being used again for testing a design concept. This is one of the devices that should be tested once removed because of its use in the circuit.

Allegro ACS756

The bulk of the electrolytic capacitors are manufactured by the Korean company, Samyoung. Some of the electrolytic through-hole capacitors associated with the mains (line) supply may be handy for spares if mains voltage projects are an area of interest.

Mains Rated Electrolytic Capacitor

The large 10 to 20 W wire-wound ceramic resistors had no signs of overheating or physical damage. These resistors may be worth salvaging even for simple dummy loads.

Wirewound Resistors

Located near the wire-wound resistors are mains capacitors manufactured by the Korean company, Pilkor. On this LG board, those capacitors were in excellent condition and worth salvaging.

Mains Capacitors

The large vertical connector, AMP series D-5200, should be considered for anyone involved with high-current designs.

AMP Connector D-5200

The circuit board is fitted are a few different types of optocouplers. One of the interesting parts is the HCNR201 which is a high-linearity optocoupler from Broadcom.

Broadcom HCNR201

Other optocouplers include Toshiba TLP781, TLP559 and TLP521. All these Toshiba optocouplers are obsolete however they may serve well as spares or for repair purposes.

Various Toshiba Optocouplers

A TE relay with the part number T92S7D12-12 is fitted to the board. This relay is rated at a 12 V at 20 A and is still actively manufactured by TE.

High Current TE Relay

Contained on the board are a plethora of remaining components to consider for salvage. These include an oscillator, heatsinks, LEDs, chokes, axial resistors and unidentified components.

Salvageable Bottom Side Components
Fitted on the bottom side of the PCB is the motor switching module (IGBT). This device is most likely not worth salvaging.

Motor Driver Module

The semiconductors on the bottom side appear to have no identification markings or those markings have become obscured by what appears to be a protective (conformal or lacquer) coating.

LG Control Board EBR369328 Bottom Side

All electronic parts on the bottom side of the board are epoxy glued to the as part of the circuit board assembly process. There is little to salvage from this side of the board because of the glue although removing components is possible with the correct tools. For low-cost and high-throughput printed circuit board assemblies, soldering using wave solder in a single pass has been a common manufacturing method. This LG board employs some solder-thieving designs in the circuit board layout as pictured below.

Component with Solder Thieving Pads

Voltage Interruption Tester for EN 61000-4-29 Updated

Introduction
This blog continues from a prior post, Voltage Interruption Tester for IEC 61496-1 Part 5. The interruption tester code detailed in that post was updated to suit supply dips or interruptions specifically to meet the standard EN 61000-4-29.

This original project was posted as a novel example of testing for changes in voltage. However, as interest in this project has been increasing specifically for the DC tests listed in the standard EN 61000-4-29, the code was changed to perform these tests only.

Code Changes
Code changes were implemented in the interruption tester for a closer approximation of EN 61000-4-29 and to improve the code portability between Infineon (Cypress) processors. In the EN 61000-4-29 standard, five tests are listed for DC voltage dips with fixed times of 10 ms to 1 s. An extract from the standard is shown below.

DC Voltage Dip Table from EN 61000-4-29

The PWM functionality in the Infineon microcontrollers, configured through the PWM component, was disabled.

Interrupt Tester Project Disabled PWM Logic

For the reduction in resources controlling the output pins between Cypress PWM and software output control, the Universal Digital Blocks (UDBs) dropped by almost 50 %.

Previous Project PSoC Resource Usage

Updated Project PSoC Resource Usage

The system timer was used as the replacement for the PWM component. Output pins that were PWM controlled are controlled directly in code. To improve the output waveform timing accuracy, the system timer was reconfigured from 10 ms to 1 ms.

Testing Code Changes
Timing control of the outputs controlling the load was performed in the corresponding function listed below.

/** *****************************************************************************
* Function Name: Output_Handler
*
* @brief Run interruption tests with timing below, 10 s separation between tests
*   Test 1 - 10 ms
*   Test 2 - 30 ms
*   Test 3 - 100 ms
*   Test 4 - 300 ms
*   Test 5 - 1000 ms
*
* @return none
****************************************************************************** */
void Output_Handler(uint8_t output_CurMenuItem, uint8_t out_statemachine)
{
    static uint8_t output_savedMenuItem;
    static uint8_t output_driver_state;
    
    if ((out_statemachine == OUTPUT_ON) && (output_CurMenuItem != 0))
    {       
        /* Handle PWM 1 Settings */
        if ((output_driver_state == OUT_OFF) || ((output_driver_state == OUT_LOW) && ( Pulse_Low_Ctr == 0)))
        {
            Pulse_High_Ctr = PWMValues[output_CurMenuItem].COMPARE1;
            Pulse_Low_Ctr = 0;
            output_driver_state = OUT_HIGH;
            V1_Driver_Write(true);
            V2_Driver_Write(true);
        }
        else if ((output_driver_state == OUT_HIGH) && ( Pulse_High_Ctr == 0))
        {
            Pulse_Low_Ctr = PWMValues[output_CurMenuItem].PERIOD1;
            output_driver_state = OUT_LOW;
            V1_Driver_Write(false);
        }
        output_savedMenuItem = output_CurMenuItem;
    }
    else if (out_statemachine != OUTPUT_ON)
    {
        V1_Driver_Write(false);
        V2_Driver_Write(false);
        output_driver_state = OUT_OFF;
    }
}

The standard EN 61000-4-29 standard states requirements for the rise and fall times when the tester is driving a 100 R load (1 us to 50 us).

Test Generator Requirements from EN 61000-4-29

The pulse duration and time between tests were validated with the load.

10 ms Interruption Tester Output

 

100 ms Interruption Tester Output

Testing showed that measured rise times were less than 18 us and the fall time less than 7 us.

Rise Time 10-90 % with 100 R Load

Fall Time 10-90 % with 100 R Load

Future Changes
To facilitate other microcontrollers, another revision of the display circuit board without capacitive sensing, a flat flex inter-board connection, watchdog and adding a third channel to the power board will be investigated.

Downloads
Listed below is the PSoC Creator project.

Interruption Tester 0.1c PSoC Project

 

Maker LED Flasher

Introduction
This blog details a prototype flasher circuit board for a school Maker community. The board design is built to accommodate through-hole and surface mount components. Featuring two component mounting styles allows the board to serve multiple uses in a school environment.

Dual LED Flasher PCB

Circuit
The circuit in the blog uses a well-worn astable LED flasher design made with discrete components. A transistor pair, wired in a common emitter configuration that drives a total of four LEDs were used. As a DC 9 V battery powers the circuit, more LEDs could be added to the design to interest young Makers.

 

LED Flasher Circuit

For the feasibility review of the prototype by the Maker community, both circuits were placed on one side of the circuit board. A single switch (surface mount) was used to control power to the through-hole and surface mount sections.

PCB
An ABS enclosure from a local supplier was initially chosen for the prototype. PCB dimensions and the mounting hole locations for the circuit board were extracted from the ABS enclosure.

Components for the flasher circuits were placed on the top layer of the board. The battery connector was relegated to the bottom layer allowing a battery to be placed inside the ABS enclosure. Routing of the board used two copper layers.

Dual LED Flasher Routed PCB

3D Printed Case
With many Makers communities having 3D printers a printed enclosure was created based on the commercially available product

3D Model of Plastic Case

The Fusion 360 and STL files are located at the end of this post.

3D Printed Plastic Case

Making
The image below shows the through-hole portion of the circuit board after being populated and partly soldered by a school student. 

Half Populated LED Flasher Board

All the through-hole LEDs and capacitors were taken from salvaged components.

To hold the circuit board in position, round head metal self-tapping screws, 3 mm between crests, 7.5 mm in length were utilised.

The surface mount portion of the board was hand populated as a second step for this blog as can be seen in the image below.

Fully Loaded Flasher PCB in 3D Printed Plastic Case

The video below shows the through hole portion of the flasher board operating.

The second image shows the surface mount section in operation during testing.

Captures from Circuit
For those Maker communities interested in checking the circuit waveforms with a oscilloscope, below are some captures taken from the transistor collector and base connections.

Voltage Measured at Transistor Collector

Voltage Measured at Transistor Base

Summary
The LED flasher detailed in this blog was published as an example for Maker communities. Available for download below is the artwork for the circuit board and the file for a suitable 3D-printed case.

Flasher Schematic

Flasher PCB

Flasher Gerber

Flasher PCB Bill of Materials

3D Case in Fusion 360

3D Case as STL*

* If the plastic case is used, 4 x round head metal self-tapping screws, 3 mm between crests, 7.5 mm long may be required.

Altium Parameter Set Example

Introduction
This blog looks at other uses for the parameter set that is available when drafting in Altium Designers’ schematics.

Example of Altium Schematic with a Parameter Set Rule

Parameter Set Requirement
An engineering pack is commonly used to convey coherent and clear manufacturing information to a production company responsible for either printed circuit board (PCB) manufacture or assemblies (PCA). Some of the information or parameters contained in the engineering pack will vary vastly between companies.  For example, some components used on a circuit board may be specified to meet automotive or military grades. Other requirements may relate to the approval of component suppliers, the custom design of a component, or factory programmed to list a few. Whilst other companies may require components traceability if certain regulations or requirements such as PSE, IEC or ANSI are needed.

The component part number may usually contain sufficient detail for the requirements detailed in the above section however in other cases, additional product information may need to be shared with the manufacturing partner.

Parameter Set Use
This blog leans on the schematic parameter set available in newer releases of Altium Designer for providing additional component information to the production company. While pushing details into the parameter set may not be considered a clean integration compared to the Altium component database, changes can be made to a project without modification to the library. Details contained in the parameter set can still be reflected in reports such as the bill of materials (BOM). This solution may be helpful for projects where minimal business investment in the project is warranted but project control using a design tool is essential. 

Parameter Set Example
For the example in this blog, the Altium Designer project ‘Mini PC’ (courtesy Altium) will be used.

Altium Example Project - MiniPC

Target Schematic Page from Altium Example Project - MiniPC

Assume for the example in this blog that the jack and relay were hand populated. The circuit board loader in this example required documentation for components that required hand population.

Example Schematic Page with No Parameter Set

A blanket rule was placed over the power jack and relay schematic components.

Example Schematic Page with With Parameter Set

A parameter set rule was added to the blanket rule on the schematic, with the custom parameter ‘Hand Population'.

Example Altium Parameter Set

An additional custom parameter set for a ‘Listed Part’, was added to illustrate that multiple parameters could easily be added to the schematic as required.

Parameter Set in Bill of Materials
When generating the Bill of Materials (BOM) in Altium, details from the schematic parameter sets are available in the BOM Properties ‘columns’.

Altium BOM using Parameter Sets

Viewing the parameter set information in the BOM generated by Altium is possible by enabling the required parameter listed in the columns section of the BOM manager. This allows customisation of the various board fabrication or assembly houses.

Extract from Altium MiniPC Project with Parameter Sets

Pictured above is a portion of the generated BOM when the ‘Hand Population’ and ‘Listed Part’ parameter set entries were enabled.

For Altium projects that have several variants, components in schematics are likely to be controlled using the variants manager. Components are marked as fitted or not fitted. When a parameter set is used, the fitting of components with parameter sets in the BOM should be reviewed.