Effective Strategies for Testing Electronic Components During PCB Assembly

Designers often find themselves challenged by non-functional circuit boards, even after painstaking assembly. Overcoming this obstacle demands more than simply pointing fingers at malfunctioning components; it requires a deep dive into understanding the essential issue at hand. Successfully navigating this landscape hinges on systematically testing electronic parts at precisely the right juncture to conserve resources and sidestep exasperation. An impetuous method may breed flawed perceptions, making thoughtful testing strategies indispensable. This discourse will delve into diverse techniques that refine the testing process, honing in on both efficiency and accuracy.

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Determining the Timing for Electronics Component Testing

The electronics industry is well-known for being highly risk-averse, a trait that deeply influences its emphasis on quality assurance. This leads to a comprehensive series of tests that components must endure to verify both their dependability and performance. These rigorous evaluations encompass not only semiconductor manufacturers but also those who produce passive components, together constituting the majority of elements within standard circuit board designs.

Figure 1: Semiconductor Wafer with ICs Undergoing Testing

Despite the fact that components usually undergo extensive testing before being integrated into a printed circuit board assembly (PCBA), certain circumstances call for additional testing. These instances may involve extended reliability assessments or intricate debug tests, serving to pinpoint defective components and uncover potential issues within assemblies. In such scenarios, engineers might explore necessary design modifications to maintain a superior level of reliability, echoing the industry's preference for faultless quality and minimizing operational risks.

During Manufacturing

High reliability applications, such as aerospace and automotive systems, often undergo additional testing under stringent safety and industry standards to ensure flawless performance. The intricate interplay of human emotions, like anxiety and pride, drives the meticulous nature of these tests. Some of these tests include:

- Thermal cycling and thermal shock testing: These tests expose the materials to extreme temperature variations, evoking a sense of endurance akin to human resilience.

- HALT/HASS testing: These tests push the components to their operational limits, mirroring a person's quest for excellence and the boundaries of human potential.

- Burn-in testing: This prolonged testing process helps identify early failures, reflecting the patience required to nurture and test human strength over time.

- Mechanical shock testing: Designed to assess the system's durability, it is reminiscent of life's unpredictable jolts that one must withstand.

These system-level tests are designed to identify failed PCBAs or individual components, so the manufacturer can recommend minor design changes. For cost-effectiveness reasons, this rigorous testing is usually only used in high-volume production and is not usually performed during the prototyping phase. Individual designers are often required to perform manual testing during board bring-up.

Testing During Debug and Board Bring-Up

Board bring-up often brings a mixture of anticipation and anxiety, especially when there's a creeping suspicion of a component malfunction. While navigating through the initial debugging tasks on a newly assembled board, one might trace an issue back to a component that seems to be the culprit. At this stage, the multimeter becomes an invaluable tool to take resistance measurements and scrutinize voltage paths across the board. Nevertheless, the question remains: once a potential fault is pinpointed to a specific component, how can it be tested effectively?

Removing Soldered Components

In scenarios where the component isn't installed in a socket but soldered directly onto the board, it must be desoldered for accurate testing. Direct probe-based tests are impractical if the component is still soldered to the board.

Components Needing Removal for Testing:

- Passives

- Transistors

- Electromechanical components (e.g., relays)

- Connectors

- Simple logic circuits

Given that these components intertwine with other board features, their correct behavior can be assessed only after removal. Post-desoldering, these components can be placed in an SMD test fixture or on a breadboard and checked for their electrical properties via a dedicated test circuit or probing system.

Figure 2: Some On-Board Tests of a PCBA can be Performed with a Multimeter

On-Board Tests with a Multimeter

Certain PCBA tests can be conducted using a multimeter, though limitations exist.

Sensitivities Involved in Component Removal

The delicate nature of desoldering components merits careful consideration. Once removed, re-soldering a component, especially if it’s a miniature part like a 0402 passive, can present challenges. Residual solder might linger, potentially creating bridges between pads. For components with fine-pitch BGAs, uniform heating with a heat gun is necessary to ensure clean removal without damage. Unfortunately, if the removed component proves functional, re-soldering may pose significant difficulties.

Considerations Before Component Removal

Here are vital points to ponder before manually extracting components for testing:

- Potential need for board replacement if re-soldering fails.

- Checking the component's datasheet for comparative graphs that align with test measurements.

Contemplating manual component extraction and testing underscores the importance of weighing the risks and referencing datasheet graphs for accurate diagnostics.

Methods for Evaluating Electronic Components on Assembled Boards

Visual Inspection

Conduct a thorough examination of the board, observing closely for any indications of damaged components. Pay attention to ICs that exhibit signs of discoloration or melted casings, which might necessitate the use of a magnifying glass or microscope to discern. This step engages the human impulse to seek out imperfections and ensure everything appears intact and unblemished.

Component Power Evaluation

Once the board is powered, employ a voltmeter to measure the voltage flowing to the components. This act not only fulfills our innate curiosity about the board’s functioning but also addresses any potential issues of inadequate power distribution. Refer to PCB footprints for your components to verify that the correct pins are being inspected.

Power Distribution Assessment

Beyond measuring power at the components, utilize a multimeter to evaluate voltage at various points within your power tree. Measure relative to the correct ground point to maintain precision and safety, satisfying the desire for thoroughness and accuracy.

Bipolar Transistor Analysis

With a voltmeter, assess the built-in voltage of BJTs on the board by attaching the meter to both the collector and emitter. Typical small transistors will measure around 100 mV. This step appeals to our disciplined approach to uncovering the nuances of technical performance.

Additional Considerations

Typically, points 4.2 and 4.3 are verified during in-circuit testing, which can be arranged with a manufacturer. While there are programming costs involved, conducting these tests internally might be more financially sensible if producing a limited batch or prototypes. More advanced examinations like signal integrity or logic tests require specialized equipment, not ubiquitously available across all PCB manufacturers. As you transition a prototype to mass production, remain cognizant of testing necessities as you collaborate with your manufacturer to initiate production.

Figure 3: In-Line Testing Detects Over 95% of Defects Requiring Rework in Manufacturing