Category Archives: Hot Wires

Mike Buetow’s thoughts on the industry

Straightforward Explanation of MIL-I-46058C for Conformal Coatings

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During your selection of conformal coating you ran in to a specification that you have seen before but not fully understood.  Conformal coating choices are vast, but with so many available, how does a user pick the correct one? Are there minimum standards that define what a conformal coating is supposed to do? Thankfully, yes there are. This column will focus on one such standard: MIL-I-46058C.

The official title for the specification is MIL-I-46058C, “Insulating Compound (For Coating Printed Circuit Assemblies).” The standard serves as a material standard, used to evaluate and document that a particular coating meets a list of specific performance attributes (more on those later). MIL-I-46058C was developed to define a uniform set of test methods and performance requirements for conformal coatings and gives users confidence that the material they select will perform.

MIL-I-46058C is managed by the Defense Logistics Agency (DLA).

DLA manages the standard and maintains the associated Qualified Products List (QPL). For a coating to be placed on (and stay on) the QPL, it must be tested annually by a DLA-certified laboratory. The data are reviewed annually by DLA to ensure that each coating proposed for inclusion on the QPL still meets the requirements of the standard. The latest version of the Qualified Products List is available from www.dscc.dla.mil.

MIL-I-46058C evaluates conformal coatings to an extensive list of properties. The tests are:

  1. Curing time and temperature: Coating must meet the requirements of the standard when cured according to the manufacturer’s instructions.
  2. Appearance: When cured per manufacturer’s instructions, coating should be smooth, homogenous, transparent, free of bubbles, pinholes, etc.
  3. Coating thickness: The recommended coating thickness shall be 1-3 mils for acrylic, urethane and epoxy coatings; 2-8 mils for silicone coatings; 0.5-0.7 mils for parylene coatings.
  4. Fungus resistance: The coating cannot support the growth of fungus.
  5. Insulation resistance: The average insulation resistance of all coated specimens shall be a minimum of 2.5 x 1012 ohms, with no specimens having a measured value below 1.5 x 1012 ohms.
  6. Dielectric withstanding voltage (DWV): Coated specimens subjected to 1500 VAC for 1 minute shall exhibit no disruptive electrical discharge (spark over, flashover or breakdown). The measured leakage current shall not exceed 10 microamperes.
  7. Q (Resonance): The resonance values for the coating, measured before and after immersion in DI water, must not change beyond specified limits.
  8. Thermal shock: Coating materials are subjected to 50 cycles of thermal shock. After thermal shock, coating must meet the Appearance and DWV requirements.
  9. Moisture resistance: The insulation resistance of the coating is measured under high temperature and humidity and must meet minimum specified values. After temperature / humidity exposure, the coating must meet the appearance, insulation resistance and DWV requirements.
  10. Flexibility: Coating is applied to a test substrate, cured per manufacturer’s instructions and bent 180° over a 0.0125” diameter mandrel. There shall be no evidence of cracking, crazing or adhesion loss of the coating.
  11. Hydrolytic stability: Coated specimens are subjected to four 28-day exposure of 85°C / 90% RH. After this exposure, the coating can show no evidence of softening, chalking, blistering, cracking, tackiness, adhesion loss or reversion to liquid state. The coating must also remain transparent enough to view nomenclature and color codes used to identify the components over which the coating is applied.
  12. Flame resistance: Coating shall be self-extinguishing and non-burning when subjected to a flame test.
  13. Shelf life: Coating must meet appearance, insulation resistance and DWV when tested after storage for six months at 25°C.

MIL-I-46058C was declared “inactive” in November 1998. This deactivation meant the standard was “inactive for new designs, except for replacement purposes.” This certainly does not mean MIL-I-46058C disappeared from the landscape. Today, MIL-I-46058C persists for coating users and specifiers due to its requirement for independent third party certification and remains the only published conformal coating standard with an associated QPL.

Caution!  As a user you have many choices of conformal coatings. Many materials claim to “meet the requirements’”of MIL-I-46058C. These are coatings have probably not been fully tested to the rigorous standard required to obtain and maintain MIL-I-46058C qualification. Treat these coatings with caution: “meets” does not mean “is” on the QPL. There is only one way to verify this and that’s through the DLA website.

The conformal coating selection process involves a check list of many variables. One of these variables is the need for MIL-I-46058C qualified coating. We hope that this article helps you understand not only how to find such a coating, but also what is behind this qualification.

Jeff Sargeant
www.humiseal.com

As We Were Saying

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And in today’s headlines from India:

  • “Foxconn Likely to Shy Away from $5 bn Investment in Maharashtra“: “Although the world’s largest contract electronics manufacturer — which makes Apple’s iPhone and iPad — had entered into a pact with the state government in August last year, the company is yet to start its production unit in the ‘absence’ of customers.”

As we were saying …

Simple Recipe to Avoid Conformal Coating Blush

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Your conformal coating film is supposed to be clear and transparent, but it’s cloudy-white and dull … it’s blushing. This condition is an indication that your coating film is trying to tell you something, and it isn’t that it’s embarrassed.  This blog will help you better understand why your conformal coating film is blushing from acquired moisture contamination and help you eliminate this defect.

Coatings appear cloudy because they have inadvertently acquired moisture, either due to their hygroscopic nature or by artificial means (a cooling mechanism created by solvent evaporation), which then reacts negatively with the coating resin –  exhibiting itself as a milky, colloidal-type substance.  Many different types of conformal coating chemistries can be sensitive to blushing under certain circumstances.  These circumstances are usually related to specific ambient conditions, application, cure, condition of the assembly/substrate/associated components, storage environment and/or equipment under use.

These conditions include:

  • High humidity, ~70% or higher
  • Low (or cooling) temperatures, ~16oC or below
  • Assemblies and associated components exposed to ambient moisture during storage prior to coating, can significantly increases the chance of blushing.  To overcome this, baking is often recommended. Not baking your boards after cleaning is a prime source of moisture uptake into assemblies
  • Storage conditions (opened containers, inside pressure pot, RH resident in the charging gas of the application equipment) and interaction with moisture already on the assembly.

In conjunction with this variety of circumstances, certain solvent-borne chemistries can aggravate this condition due to the fast evaporation of internal solvents.  This creates a cooling mechanism as they volatize from the film.  This cooling mechanism will condense any moisture vapor that may be present in the immediate atmospheric area.

High solids, low volatile room temperature vulcanized, or UV conformal coatings (with secondary moisture cure functionality) may also show some degree of “blush.” They are more sensitive, possibly hygroscopic, to the presence of ambient moisture vapor as this is utilized to activate their primary or secondary curing mechanisms.

Problems that can be created due to moisture vapor intrusion/blushing:

  • Surface tackiness/incomplete cure
  • Below standard aesthetic quality
    • Coating discoloration
    • Poor gloss retention
  • Poor adhesion
  • Wrinkling during second coat application/over-coating.

Here are some simple steps to start with … DIY:

  • Maintain nominal ambient humidity in the production environment between 45% and 65%.
  • Maintain nominal ambient temperature in the production environment between 18oC and 27o
  • Increasing the flash time between coating application and cure may help, as moisture vapor in the wet film may have the potential to re-evaporate
  • Use different thinner to change evaporation rate.
  • Use desiccated air/nitrogen to push coating through applicator
  • Post-bake assemblies after aqueous wash (if applicable) to eliminate any entrapped (under or between components) moisture.
  • Ensure that all partial containers are properly sealed when stored. Nitrogen purge in partially used container helps to eliminate moisture.

We hope that this helped you understand what blushing is, how it occurs, and how to prevent/alleviate it from occurring.  Remember that moisture is the root cause of cloudy or blushing conformal coating.  With many potential sources of moisture contamination, following our simple recipe will lead you back to a crisp, clear, and transparent film, and zero defects.

Nick Naumovic

www.humiseal.com

Filipino Fiasco

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The situation in the Philippines is starting to feel a lot like that of Turkey from July of this year: A paranoid leader turned strongman seeks to exert his supreme dominance over a democratic nation.

Will the country stand back while Philippines President Rodrigo Duterte effectively declares martial law? Or will the army — no fan of China — assert itself and ironically return law and order to the nation by overthrowing a budding dictator?

There are more than 30 EMS companies in the Philippines, the largest of which include IMI, ranked 28th worldwide in EMS revenue at $800 million last year, EMS Components Assembly ($110 million), and Ionics ($63 million), which has seven plants there.

Other major players with smaller operations include Siix, Celestica, Cal-Comp and Wistron.

Although US-centric for decades, the Philippines under Duterte are pivoting toward China. US companies have invested nearly $5 billion in the country; even if they no longer feel welcome, extracting that won’t be easy.

Either way, politically the Philippines are a complete mess. Duterte has taken a stable nation and completely disrupted it, without any clear end-game. If his goal was to expand his nation’s markets and hedge its bets — understandable, given their neighborhood — he could have done so in a much simpler fashion. As it stands, he has alienated many of the Philippines primary trading partners, and for what? Business partnerships don’t have to be a zero-sum game. He could have ramped his dealings with Beijing without destroying his relationship with Washington.

Duterte likes to rail against the West for being what he considers corrupt and hypocritical would-be overlords. His own military very well appreciate the security the West historically has provided, however. His words might play well with the public, but he could very well pay the price with his life.

 

Racing to Failure?

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Reuters is reporting that Samsung has temporarily suspended production of the Galaxy Note 7 smartphone after replacements for the first batch of devices also proved to be almost as good at spontaneously combusting as they are at surfing the Web.

One brand manager went so far as to compare the self-igniting smartphones to the Ford Pinto, whose rear-end fuel tanks had the unfortunate tendency to explode upon contact.

Samsung’s situation isn’t unique: Apple experienced similar problems with previous iterations of the iPhone. But given the speed with which new phone models are brought to market, one begins to wonder whether these defects are part of a larger failure of the process itself.

Is is possible we’ve reached an inflection point whereby, in the rush to get product to market, the validation phase is — pardon the pun — being short-circuited? Are suppliers properly vetted, product thoroughly tested, risks appropriately balanced?

Or has consumer electronics reached a point where it’s a race not to market but to failure?

Oct. 11 addendum: The Korea Herald and others are now reporting Samsung has decided to pull the plug completely on the Note 7. The estimated cost: Billions.

 

 

Foxconn India: Still a Pipe Dream

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It’s been a year (more actually) since India announced — to great fanfare — a memorandum of understanding with Foxconn to invest $5 billion over the next five years in the nation. For India, it seemed like a marriage made in heaven: the world’s largest electronics manufacturer would be an ideal partner for its goal to develop a local end-to-end supply chain that could not only serve its burgeoning domestic population but also provide a steady stream of exports to the rest of the world.

Yet as the Times of India points out today, the bride is still waiting at the altar.

As we said at the time, Indian officials shouldn’t hold their breath waiting for the relationship to be consummated. Foxconn is really good at promising huge investments, only to fall short in the end.

Actually, we’ve been saying this for years. Foxconn is Chinese to the core. It may on occasion have dalliances with other countries, but it always returns to its mate. Suitors, take note.

 

What’s the Deal with Delly?

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Gayla Delly left Benchmark with no notice last week. Why?

Changes at the top of Tier 1 and 2 EMS firms don’t happen often. Before Friday, in fact, Benchmark had had just two chief executives in its 30-year history.

Cary Wu founded the company as part of a buyout from medical device manufacturer Intermedics in 1986. He remained in charge until December 2011, when he promoted Delly, the company’s longtime head of finance, to the top spot.

Highly dependent for years on the high-end computing sector, especially IBM, Benchmark had been trying to balance its portfolio via acquisitions. With its acquisitions of Suntron and the EMS operations of CTS, both in 2013, the company attempted to broaden its reach into the high-reliability industrial, medical and aerospace/defense markets. It then snapped up industrial communications OEM Secure Technology in 2015.

Many bigger EMS acquisitions are slow to be accretive. The large amount of fixed assets and (typically) lower capacities at the acquired company mean layoffs and restructuring costs will follow. Still, investors are impatient and the deals were met with criticism in some quarters.

Much like Sparton and its now-departed CEO Cary Wood, Benchmark faced strong opposition from a loud activist investor who accused the EMS company of poor fiscal management. (Interestingly, unlike many of its similar-sized competitors, Benchmark has typically been patient with its M&A strategy, choosing to keep its debt levels low.)

The intensity of that criticism, which was public in the spring, had quieted down during the summer after the investor won two board seats. On its quarterly conference call in late July, Delly went to far as to deny any strategic changes in the direction of the company following the seating of the new directors. This makes the timing of Delly’s departure all the more curious.

Last Friday, the announcement came that Delly was being replaced as president and chief executive with veteran electronics executive Paul Tufano, effective immediately. Tufano is a Benchmark board member who has spent more than three decades in the technology and telecommunications industries, most recently as chief financial officer of Alcatel-Lucent. He also has a background in EMS, having been executive vice president and CFO of Solectron. It’s possible the move implies the company will refocus its sights on computing and telecom. We shall see.

Neither Delly nor the company has yet commented on the change.

 

Auto Electronics: Gearing Up or Headed for the Cliff?

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What would the electronics industry do if automotive demand were to pull a Thelma and Louise and head off the proverbial cliff?

The auto recovery has been the axle of the Western supply chain since 2008. The drivetrain is starting to show some wear, however, with market followers forecasting nominal growth at best for 2016.

The good news is that electronics content in vehicles continues to increase, rising to 8.9% of the $1.42 trillion worldwide electronic systems market last year, up slightly from 8.6% in 2014. Moreover, forecasts call for the share to continue to rise over the next several years.

Less clear is the extent, if any, the seers account for the potential for widespread ride-sharing trends or — worse for some — outright banning of vehicles.

To wit: Some 27 million Americans alone will use some form of ride-sharing at least once this year, a figure that doesn’t include traditional car-pooling. Urban millennials are growing up without the preconception that vehicle ownership equates to status, an important cultural shift.

A drop in demand for hybrid/electric vehicles (HEV) could also decelerate electronics growth. Hybrid sales alone dropped 15% year-over-year in 2015 — reversing a big gain in 2014 — and bottoming oil prices have kept the market for electric sluggish. Hybrids carry almost twice the electronics content of conventional gas autos, making HEVs a key growth engine for electronics makers.

More disconcerting to the auto supply chain is the prospect of a carless environment. This is actually happening, and in places you wouldn’t necessarily associate with technological backlash. For example:

  • Bogota, Colombia, has been car-free on Sundays since 1976, a move that sidelines an estimated 1.5 million vehicles.
  • Likewise, Jakarta has sponsored Car Free Day every Sunday since 2007.
  • San Francisco shuts certain streets to vehicle traffic on various Sundays throughout the year.
  • Oslo plans to ban cars from the city center by 2019.

Car-free days are becoming so widespread, the phenomenon has its own Wikipedia entry. In fact, now there’s even a World Car Free Day (Sept. 22).

The electronics supply chain has gotten plenty of mileage from the automotive industry for nearly a decade. It might be time to find a backup plan, however, if the sector wants to keep trucking on.

What Do You Do If You Can’t Have Reference Designators?

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The first answer to that question is probably going to be along the lines of, “Put them on the board.”

But, sometimes you can’t have reference designators on your board. Maybe it’s too densely populated and there isn’t room. Maybe, for aesthetic reasons, you’ve chosen to leave them off. With some products, like development boards, it’s sometimes necessary to use the space for instruction or functional identification and reference designators would confuse your customers. 

It’s always best to put reference designators as close to the part as possible, and on the same side as the part, but if that’s not possible, you can still create an assembly drawing. When laying out the board, put the reference designators in a different layer than the text you want in silk screen. Then, create a PDF that has all the component outlines in their place, with reference designators. Make one for the top and one for the bottom. Call this document “assembly drawing” and include it in the files sent in to be manufactured.

Figure 1 shows a good assembly drawing format. It has reference designators and polarity marks.

You might ask why reference designators are needed when all the surface-mount parts are machine-assembled. First, any through-hole parts are hand-assembled. Their locations and board side needs to be clear for the people stuffing them.

Second, CAD systems don’t always have 100% accurate information. If the center point of the footprint is off, surface mount machines (ours and anyone else’s) will center the part where file says to put it, which, in the case, would be the wrong spot.

The reference designators are also part of quality control. It’s another opportunity to remove ambiguity. Ambiguity bad. Certainty good.

Duane Benson
Car 54, where are you?

http://blog.screamingcircuits.com/