Im-PART-ing Knowledge: Live and Learn Product Assembly

Im-PART-ing Knowledge: Live and Learn Product Assembly

By Douglas Alexander, Component Engineer
Special to Footwasher Media

A few years back, an employee of a capacitor manufacturer left the company and stole the formula for a low equivalent series resistance electrolytic capacitor. He brought the formula to a black market operation and began to produce the capacitors using the same markings as the original company.

As it turns out, his bogus operation did not get the formula right and produced millions of bad capacitors that were sent all over the world. My company was one of the unfortunate recipients of the bad caps and we had to spend thousands of dollars and hundreds of hours reworking boards, removing the bad counterfeit capacitors, and replacing them with the good parts. Had we performed an incoming inspection based upon what is known as an Acceptable Quality Level screening, we would have caught the bad parts and saved ourselves a lot of money and grief.

Over the years companies have developed a systematic approach to the business basics of components and product assembly, often from the hard lessons of costly errors. And now, there are new technologies being introduced to detect counterfeit integrated circuits (http://tinyurl.com/4xw8555) and companies are being formed for the sole purpose of screening for counterfeits (http://tinyurl.com/3g3ynve).

Processes

Component selection: The task of identifying a “correct” component for the circuit may involve an understanding of how the circuit works and extrapolating the correct parametric for a device or it may involve identifying the device from a given “list” of parameters. The latter case may be presented as: “I need a low drop-out regulator that can handle 500 milliamps with a 5V input and 3.3V output.” The individual responsible for identifying the final component must also know what questions to ask the Design Engineer in order to expedite the selection of the right part. Is there a package preference, a preferred mounting configuration, an operating temperature consideration, a size constraint, or any number of other factors that may affect the final selection?

Testing: Screening is often required to verify that a device meets the manufacturer’s specifications and functions as expected in the design process or existing circuit under test. This can be as simple as verifying a resistor's value and tolerance on an LCR meter (Inductance/Capacitance/Resistance), or it can be as involved as qualifying a higher-level, purchased assembly that has hundreds of critical parameters.

Analysis: This may involve what is known as Failure Mode Effect Analysis (http://tinyurl.com/3hhdj6g )where a component is found to be the cause of a failure in a circuit. Every failure must be examined for “Root Cause” in order to understand the fundamental reason for the failure. Until this is understood, there can be no assurance that the failure will not occur again. To say a component failed because of excessive electrostatic discharge (ESD) (http://tinyurl.com/44xap3d) does not delineate the full causation of the failure. How much of a charge is needed to destroy the device? What was the source of the ESD? How did the charge reach the component? Is the circuit protected against ESD? (http://tinyurl.com/3sy42d8) These questions and many others must be asked in order to determine the ultimate “fix.”

I once had to stop a production line because a high incidence of board failures was detected just before the next level assembly step. The problem was a dramatic drop in the output power level for a two-stage amplifier board. Our technician traced the problem to the same component on every failed board. After one week, I received a very apologetic call from the manufacturer who said the root cause of the module failure was due to a training oversight for a new employee assigned to the bonding operation. The employee had been wire bonding the output of the first amplifier to the output pin of the module rather than to the pad on the input of the second stage amplifier. We purged our stock and the problem was resolved. The root cause was bad training management at the manufacturer’s company.

Reliability: Reliability is the property of a device or circuit that determines if the component will function as designed for an expected amount of time under stated, worst-case operating conditions. Every component's lifespan is characterized in three major stages: infant mortality, useable lifetime and wear out. In most cases, all three can either be charted using manufacturer’s specifications for reliability or can be determined through actual testing known as Highly Accelerated Life Testing or Highly Accelerated Stress Screening, which increases the stresses that would precipitate a component failure. It is common knowledge that for every 10 degrees Celsius increase in temperature, a capacitor’s lifetime is reduced by 50%. Heat is the most common source of stress, and every circuit generates some increase in temperature over ambient causing various levels of additional stress on components.

Availability: If a component is perfect for the circuit, but is made of “unobtanium,” (unavailable), then all the effort of qualifying a component up to this point is to no avail. On more than one occasion, I have worked with engineers who have designed from preliminary datasheets. When it came time to build the first boards, it was discovered that the manufacturer was not yet producing the parts for sale. Understanding components will enable you to identify multiple alternate components and sources for many devices. The reason is obvious: if a circuit is designed with parts that cannot be found in quantity, the manufacturing process comes to a halt and cannot be restarted until that circuit is redesigned or a substitute component is identified.

Suitability: This criterion concerns more than just the physical form, fit, and function of the component, but relates more with business issues that, without some investigation, may not be obvious at the time of selection. The examples are many: the supplier is not reliable, the datasheet designates preliminary status, (see previous paragraph), the manufacturer attaches royalties or license fees that may escalate the product cost beyond marketability or cash flow management capabilities, there are minimum-buy quantities that are unrealistic for low volume, high mix operations, and any of a myriad other business related applications. These should all be addressed and resolved in a concurrent review with all affected departments.

Affordability: This is the overall cost associated with the component under consideration. With rare exception, given the same time-to-market window, additional features translate to additional costs. You may find a part that costs the same or a bit more, but adds extended features that will give a company an edge over competing products. But, if a more expensive part is selected that has additional features that are not critical to marketability, then the better choice may be to scale back the design and select a cheaper component with the minimum feature set. Affordability looks at the marketplace and decides if the company is going to get the most return for their investment.

Traceability: Components and products are always changing. Manufacturers may or may not send out a Product Change Notice every time a form, fit, or function change is implemented by the manufacturer. The Design Engineers may not be aware of End of Life announcements, IC die revisions or mechanical dimension changes that could affect the physical or electrical characteristics potentially impacting the product performance by compromising the integrity of the design. It is important to stay current with every component in a product assembly. This means every component should have a Specification Control Document or a Purchasing Specification Document that includes both revision level control and all manufacturer or vendor change notices associated with that part.

Those are some of the basics concerning the business aspects of components. In subsequent discussions, I will publish what we'll be calling the 411's on various types of components. These will be as mentioned earlier and shown for example at the Components Engineering Learning Center (http://tinyurl.com/3sy42d8).

Douglas Alexander has been working in the electronics R&D and manufacturing sector for over 25 years with experience in all aspects of component selection, qualification, verification, specification control, reliability prediction, and assurance. His goal in Componentsengeineering.com (http://tinyurl.com/4xd8oaw) is to offer the reader a comprehensive understanding of the various types of electronic components used by designers and manufacturers who are associated with electronic engineering and manufacturing. ■