When commercial AOIs were not up to the task, a little internal ingenuity saved the day.
While there is great debate in the quality community as to who first made the observation that visual inspection by humans is not 100% effective (both W. Edwards Deming and Dr. Joseph M. Juran have been given credit) and even some debate about the true effectiveness rate (is it 75%? 80%? 85%?), all agree it is inefficient and error-prone. Yet, automated optical inspection is often deemed not cost-effective for relatively simple processes in many factories.
One area that is often problematic for electronics manufacturing services providers is odd-form part through-hole insertion. Through-hole odd-form parts continue to be used when a part’s weight or need for a more robust solder joint makes that level of interconnection more reliable. Transformers, large capacitors, diodes, relays, connectors and pressure sensors are few examples of parts that are often still packaged as through-hole. Manual assembly, like manual inspection, is prone to variation and associated defects, particularly issues such as misaligned parts, missing parts or wrong parts. Odd-form parts are typically of a size or shape that makes automated insertion methods impractical.
As we venture out among the aerospace industry, it helps to know the lingo.
Four years have elapsed since we last provided discerning readers with a helpful field guide to the major species inhabiting trade shows. Four years is a long time. Has anything changed? Have the major species evolved? Regressed? Have some gone extinct or suffered outright obsolescence? What are the replacements?
The quest for knowledge beckons us back to the field.
Curiosity about a changing world and an evolving industry propels us to don pith helmets and binoculars and return to the source. Post-graduate work commences now.
Will IPC accept the >50% voiding recommendation?
We have long had numerical guidelines for voiding levels below which we deem acceptable for BGA joints. Originally from IPC documentation, the limit called for less than 25% voiding of the joint area when the joint is looked at from the top-down in x-ray. More recently, and entirely because of evidential data, this has been increased to 30%.
Many other joint types also given designated qualifications in the IPC guidelines, such as through-hole joint fill levels, can be evaluated using x-ray. However, there has always been an anomaly in the level of voiding in bottom termination components (BTCs). To date, no evidence-backed, indicative values are published detailing acceptable voiding in these joints and, in particular, the large central pad under QFNs.
Solvents in holes can heat and "pop."
This month we look at voids or missing conformal coating. Depending on the lack of coating and position, this condition may result in acceptance or rejection. Normally with conformal coatings, small voids not specifically associated with electrical termination or bridging connections are acceptable, depending on the level of inspection criteria.
FIGURE 1 shows voids or bubbles in conformal coating under UV dark light. I would suggest both these cases require rework, as the electrical termination points are exposed, and there is no protection. Most likely, solvent coating has run into the holes. As the coating starts its first transition from a liquid, the voids expand from the holes. Then they pop, leaving the surface or pads with no protection.
It is suggested too much coating was applied on one pass, and initial evaporation could not occur, resulting in a volcano-like reaction from the holes. Each of the holes associated with coating voids had limited solder fill or cavities. In the past, we have seen the same problem with selective coating around press-fit connectors.
Which holds up better: mesh-mounted or mechanically tensioned, mesh-free frames?
Ah, stencil tension. A subject near and dear to my heart and one I’ve written about before in this space. In fact, we covered the subject a few years back, when we discussed how the loss of tension on a conventional mesh-mounted stencil can adversely impact printing results and why other solutions may prove superior. In recent years, studies undertaken to evaluate the impact of stencil tension on print performance have, indeed, confirmed these assumptions.
Before we get into the outcomes of our company’s work, let’s review the basics of conventional mesh-mounted frame stencils and mechanically tensioned, mesh-free frame systems. To be fair, mesh-mounted stencils are the industry standard. They are the predominant stencil type employed for electronics assembly. The alternative approach is mechanically tensioned, single-frame solutions that allow manufacturers to use one frame alongside multiple foils for various assemblies.
Do you know the quiet leaders? Often they are the ones who get things done.
In 1981, when I started in the electronics manufacturing services (EMS) industry, two things really surprised me. First was that EMS factories saw tomorrow’s tech before the rest of the world. Second was the amazing amount of knowledge resident on the factory floor. That second point always drives me to challenge folks who believe it is impossible to succeed without a college degree. As long as I’ve worked in EMS, I have been exposed to factory workers who learned on-the-job the same things I did in college.
A couple months ago, I had a great conversation with Lois Kenon, a rework/repair specialist at TeligentEMS in Havana, FL. She went to work in the service sector after high school, planning to try a few jobs before going to college, but ended up staying in manufacturing. We spent time talking about her leadership philosophy, and I felt it made sense to share some of that philosophy in my column.