©vektrex 2014; 1 introducing n+1 load board topology february, 2014

©Vektrex 2014; www.vektrex.com 1

Introducing n+1

Load Board Topology

February, 2014

What Makes A Load Board Successful

Properties:

• Flexible to support testing of multiple sizes and types of devices• Efficient, reliable electrical connections• Support for series drive to reduce wiring and drivers needed• Individual device selection for measurements• Simple to design and manufacture• Low thermal resistance to provide for small temperature rises and

good temperature uniformity• Standardized across all company departments• Easy to work with – load, secure, maneuver and handle…etc.


The Load Board Circuit Topology Influences Reliability System In Many Ways

• Topology – the way LEDs are connected and powered

• Circuit board routing on load board printed circuit boards

• System wiring from drivers to load boards

• Connectors in reliability chambers

• Switching systems used for measurements


Circuit Topologies

• 2n provides 2 connections for each LED

• 4n adds 2 more to support 4 wire (kelvin) voltage measurements


2n and 4n Topologies Increase System Cost

• Individual circuits for each LED increase wire count• Copper wire costs can exceed 10-15% for reliability systems

designed with 2n and 4n topologies

• Many connections on load boards = large expensive connectors

• 2n and 4n circuits complicate PCB layout, usually multiple layers are required

• Switching systems are more complex with 2n and 4n topologies


n+1 Simplifies Circuit, Reducing Costs

• 2n provides 2 connections for each LED

• 4n adds 2 more to support 4 wire (kelvin) voltage measurements

• n+1 places LEDs in series circuit to minimize connections


Topology Comparison


4n 2n n+1

Load Board PCB Layout Multilayer Usually Multilayer

Single Layer

Connector Pin Count 40 for 10 LEDs

20 for 10 LEDs

11 for 10 LEDs

Connector Type Multiple Double Sided

Double Sided

Small Single Sided

Series Drive Requires External

Connections

Requires External

Connections

Built Into Topology

Drive Cable Wires 40 for 10 LEDs

20 for 10 LEDs

2 for 10 LEDs

To Support Large Scale Testing 8 Groups Of 10 LEDs Are Placed On A Single Load Board


The LED Groups Can Be Powered With Just A Few Wires

LED Group 1 LED Group 2 LED Group 3 LED Group 4

Load Board 80 DUT Type

Pin 44

Pin 1

LED Group 5LED Group 8 LED Group 7 LED Group 6

SpikeSafe 2008 ChannelPulsed/DC

Current Source

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Channel 7

Channel 8


Two Drive Wires Used Per Connector For Reliability / Stress Operation

Dual Connectors Allow A 1-Layer PCB Design

• Dual symmetrical connectors allow 1 layer PCB design


Example Design - Surface Mount Devices


Example Design - COB (Chip on Board) with screw down


A Single LED Can Be Isolated For Measurements

• 4 Wire Connection Maintained To Edge Of Load Board


n+1 Topology Forms The Foundation For The Highest Performance Load Boards

• Simple circuit

• Low pin count

• Reduced cable wire count

• Flexible, supports many different kinds of LEDs

• N+1 is standard in Vektrex reliability systems


©vektrex 2014; 1 introducing n+1 load board topology february, 2014

Documents

n topologies vektrex

connections vektrex

single load board vektrex

n circuits

edge of load board vektrex

load board topology

wires vektrex

topology comparison