Developing Manufacturing Test for Electronic Products

Contributed by: Arijit Karmakar, Cypress semiconductors

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As discussed earlier, traditional manufacturing test fixtures have a bed of nails inserted into holes in an epoxy phenolic glass cloth laminated sheet (G-10). The bed of nails consists of an array of small, spring-loaded pogo pins which are aligned such as to make contact with test points or GPIOs on a printed circuit board and are also connected to a controller board using wires. Sensors are placed on the top and/or back panel. The top panel locks into the bottom panel using adequate mechanism to align the sensors to components on PCBAs. The top sensor panel shall be customizable either with a linear displacement option or modular (pluggable model) to cater different component arrangement/placement across PCBAs. This bottom panel can be modified for each board depending on the number of test points and PCB dimension. The units are placed against the bed of nails and pressed downwards manually or by means of vacuum. All the key hardware components are then tested manually with human intervention or using an automated tool.

Figure 2 Mechanical design of the Manufacturing Test Fixture
Figure 2 Mechanical design of the Manufacturing Test Fixture

The spring loaded test probes used for implementing bed of nails are chosen with proper tip styles, plating, spring forces as per requirement. The internal spring exerting force on the probe tip should be selected depending on the surface finish of the test target or else the higher spring force damage the components on board. Serrated, Cup shaped or crown shaped probe tips are used normally to test component leads. To test terminal points, slotted cup or flat shaped probe tips can be used. Spear, sharp chisel or needle shaped probe tips are recommended to use for testing pads which ensures increased tip contact pressure for reliable testing. To test plated through holes or vias, chisel or arrow head probe tips and for solder beads/bumps/domes micro-serrated probe tips can be used.

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Figure 3 Arrow head pogo pins
Figure 4 Flower head pogo pins
Figure 4 Flower head pogo pins
Figure 5 Top pressure plate with press down Nylon rods
Figure 5 Top pressure plate with press down Nylon rods
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Figure 6 Enclosure/housing for the test hardware

Different tests ranging from voltage range measurements, LED color and intensity measurements, Capacitive touch functionality, audio testing, USB and other serial port functionality and RF measurements are done inside the test fixture. In case automated manufacturing tests, apposite sensors are used to validate the components on board, like color sensor for RGB LED and electromechanical units like solenoids, relays, servo motors and actuators to activate or test switches. Compared to manual and semi-automatic methods, automated test methodologies are less susceptible to any false pass or miss (caused mainly due to human error) during testing. Although automated manufacturing test facilities are pretty expensive, industries prefer to go for them as they can improve the testing time and coverage for each product considerably.

Today’s manufacturing tests incorporate high level of complexity managing multiple device firmware in multiple PCB boards. In adhere to that, the test programs are frequently being ameliorated to comply with production changes or to fix bugs in firmware. The task of managing the variability and changes in manufacturing test process is arduous and fallible in particular when testing and production are done off-site. Proper change management system and version control tool obviates any fault or issues which might impede the manufacturing process.

With the advancement of electronic industries, products are becoming smaller with increased functionalities and the requirement for testing each and every part of the system are becoming very critical. Traditional methods require enough room to place probes and seemingly appear very difficult in case of designs with fine pitch parts, particularly with embedded components. The paucity of proper testing tool and mechanism has led the industry to seek for new techniques and alternate method of testing.


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