My latest editorial considers the disconnect between reports of future investments Foxconn and what actually comes to pass. Too often, the astronomical sums reported don’t ever turn into real new employment.
Sometimes, in PCB assembly, it’s not the layout of the SMT PCB that creates issues, but the design of the part itself, or the plan for the part’s location, given its dimensions. We have to ask ourselves, sometimes, “What were they thinking?”
In this case, a customer’s BoM called for a part (an RF200 module with through-hole pins) to be mounted onto a PCB. At one end is a bulky SMA connector that due to its size exceeds the thickness of the module. The SMA connector faces inward on the PCB; it’s not mounted to hang over the edge. As a result, the SMA connector bottom side touches the board and props one end of it up; it doesn’t permit the module’s pins to be properly inserted into their corresponding PTH barrels on the board. One end of the SMA is pointing upward on an angle like a missile-launcher.
This is obviously not acceptable in circuit board assembly; not only is customer access to the connector compromised, but the module cannot be mounted in a planar fashion and having some of the pins fully inserted and some halfway out of the barrels, with one end of the module elevated, is certainly not acceptable.
The fix was relatively easy; we recommended that the customer allow us to use two single-row socket pin adaptors to provide the standoff necessary to keep the SMA connector from touching the board while at the same time allowing easy and unobstructed access to the connector.
Two socket headers were used, corresponding to the module’s two rows of pins. Not only did this provide the needed standoff, without creating any other issues, but it also allowed the customer the potential for removing or replacing the module in the socket pin adaptor in the future without serious rework issues, since it’s a mechanical mounting. It’s also a robust electronic assembly connection in terms of strength and durability, and the module is completely planar with the surrounding PCB surface.
We are seeing a warming trend in the solar industry, with Flextronics, Celestica and others publicly talking up the renewable energy sector.
In Juárez, Flextronics’ manufacturing plant has reached its maximum capacity production of 1.3 million solar panels a year.
Meanwhile, Celestica poured millions of dollars in the June quarter into ramping production for solar lines in Asia. Speaking to analysts on July 23, CFO Darren Myers said, “[W]e think there is a lot of exciting opportunities for us within solar.”
It was just five years ago when the solar industry was growing like gangbusters, fueled by massive government investments and incentives. Then came the crash in 2012, which prompted some conglomerates to offload units (read: Dover) that had become dependent on those markets.
But the market has heated up again. In the US alone, one major trade group believes the installed solar panel capacity will double, to 40GW, between in 2014 and the end of next year. Another industry watcher forecasts a 36% gain worldwide this year alone.
Whether the gains will sustain themselves after US government tax credits on home installations run out is anyone’s guess. For now, at least, EMS companies are once again basking in solar’s warm glow.
It is hard to believe that in July we will celebrate the 9th anniversary of the advent of RoHS. So the timing seemed right when I was recently asked to speak at the Boston SMTA Chapter on The Status of Lead-Free 2015: A Perspective.
An overview of the entire 75-minute presentation would be a bit long, so I am going to discuss three of the “questions” that I covered.
- Q: We are now almost nine years into RoHS’s ban on lead in solder. How has lead-free assembly worked out?
A: Something over $7 trillion of electronics have been produced since RoHS came into force, with no major reliability problems. One senior person, whose company has sold hundreds of millions of lead-free devices since 2001, reports no change in field reliability. The challenge that implementing lead-free assembly placed on the industry should not be minimized, however. Tens of billions of dollars were spent in the conversion. In addition, failure modes have occurred that were not common in tin-lead assembly, such as the head-in-pillow and graping defects. But assemblers have worked hard with their suppliers to make lead-free assembly close to a non-issue. Some people ask how I can say that lead-free assembly is close to a non-issue. My office is across the hall from some folks that purchase millions of dollars of electronics a year for Dartmouth. Several years ago, I asked them how they feel that electronics perform since the switch to lead-free. They answered by saying “What is lead-free?” If people that buy millions of dollars of electronics have not even heard of lead-free it can’t be a big issue.
- Q: In light of sourcing difficulties, is there an industry consensus regarding lead-free conversion for military, medical, aerospace etc. assemblers that will continue to be exempt?
A: The main issue is getting components with tin-lead leads, especially BGA balls. Many assemblers are reballing BGAs, which has become a mature technology, although with an added cost. As years go by and there becomes more confidence in medium to long term lead-free reliability, some exemptees may switch to lead-free. However, I think mission critical applications with 40-year reliability requirements must be extremely cautious to make the switch. There may be subtle reliability issues that may show up in 40 years, that are not found in accelerated testing. One concern is aging. Even at room temperature, solders are at over 50% of their melting temperature on the absolute scale (300K/573K = 0.52). So aging can occur at room temperature. Some research suggests that lead-free alloys may be more affected by aging than tin-lead alloys.
- Q: It has been said that you claim that lead-free assembly has some advantages. Can this be true?
A: Guilty as charged. Lead-free solder does not flow and spread as well as tin-lead solder. This property can result in poor hole fill in wave soldering and some other assembly challenges. However, this poor wetting and spreading means that pads can be spaced closer on a PWB without the concern of shorting as seen in the image below. Your mobile phone would likely be bigger if assembled with tin-lead solder.
Photo courtesy of Vahid Goudarzi.
Double-sided SMT PCBs are usually no problem to solder; two passes, and the bottom-side components are held in place with SMA adhesive. But occasionally, a large or heavy component on the bottom side, such as an inductor, poses a problem because it will drop off during top-side reflow.
In one particular case, an inductor with an open bottom (with inner coils visible) couldn’t be fixed in place with adhesive. Its two pads didn’t have enough solder surface tension when liquidus to hold it to the bottom side of the board during the board’s second run in the reflow oven with part turned upside-down. What to do?
The solution was a universal reflow fixture with support bars, located beneath the part to support its weight during reflow so that it would not pull loose and drop. The fixture had to hold it firmly in place and in location during the second pass through the oven.
Other solutions were either unsuitable or added an extra process step. The use of adhesive, as mentioned above, was not practical, since there was little available component body to attach to, and one did not want any foreign material, i.e. adhesive, to get inside the component body with the exposed coils. Nor was the use of a higher-temperature solder practical; the component is a standard part and simply needed to install with the other components without additional steps or complications.
Adapting the universal fixture to hold the inductor in place was an easy matter. The flexibility of universal fixtures is such that they can be adapted to support a wide variety of component sizes and shapes effectively across a wide range of board sizes, layouts, etc. They are also much less expensive than a custom fixture, and readily available for use. Consider this in contrast to an expensive custom fixture that will require on average 2 to 5 days to fabricate.
The universal fixturing will do the job, and be reusable: it’s a one-time investment that can be used over and over for a multitude of different assemblies. Saving production time and tooling costs has a positive effect on profitability, and at the same time, the highest level of product quality and reliability is maintained. Obviously, not all assemblies require fixturing, only those with special requirements like this one that cannot be processed as simply as most SMT assemblies can.
We love parts on reels. Who doesn’t? But reels aren’t always practical — and it’s not just about cost. Cost is, of course, important, but there may be other factors to consider.
Say, for example, you need 20 2.2K Ohm, 5% 0805 resistors. You could buy a small strip of 25 from Digi-Key for $0.32. That gives the 20 you need, plus a few spares just in case.
Alternately, you could buy a digi-reel ( a custom quantity reel). On the reel, you’ll probably want more parts to keep the strip long enough for the feeder. Let’s go with 250 parts for $1.39. Digi-Key charges $7 extra to create a custom reel, so that’s a total of $8.39. Still peanuts.
For a third choice, you could just buy a full reel of 5,000 for $10.64. Still peanuts. If you’re gong to need the same part for a lot of designs, this might make sense. But, there’s more than just cost to consider. You need to store and ship it. Shipping two dozen reels gets pretty expense. Storing and inventorying several dozen reels can become a hassle too.
The beauty of Digi-Key, Mouser and other places that sell cut strips is that they essentially become your parts warehouse. You pay the 32 cents and never have to worry about whether the part is in your inventory, how many are in your inventory, digging it out of wherever you stuffed the reel when you last needed it.
If you do buy and store the whole reel, you don’t need to ship the entire reel to us. Just cut a strip with the number you need, plus about 5% for that “just in case.”
Of course, if you need a few thousand of the parts go ahead and send us the reel. It would make sense then.
Reel, reel your part
Solder it, solder it, solder it, solder it
Cost is but a factor
This isn’t directly related to printed circuits but oh-so-cool nonetheless.
NASA this week snapped this photo of (ex) planet Pluto (shown with its largest moon, Charon, at the left), proving once again that man is capable of remarkable engineering feats:
This shot was taken by the New Horizons space probe from a focal point several million miles away from the dwarf planet, which seems like a lot only until one considers the ongoing nine-year long trip has taken the probe nearly 3 billion miles from Earth.
Congratulations to the NASA and Johns Hopkins APL team that conceived and executed this mission, and to those behind-the-scenes designers and manufacturers that built this one-of-a-kind system.
Manufacturing, especially small volume one-time-only builds (like a prototype) is hard. It’s not wise for most people to actively seek out chaos, but that’s what we do, and we do it wisely. That’s what we’ve been doing since 2003.
We do it because it’s hard and because it’s necessary.
A big part of quality manufacturing involves risk reduction. Prototyping and quick-turns inherently add in a lot of risk. While we’ve designed our processes and systems around turning that risk into a quality product, there are a few things that you, the customer, can do to help reduce risk even further.
One of the best things you can do to reduce risk is to prepare a well organized kit, as shown in this video:
You can send us your parts in short, cut strips, like you get from Digikey or Mouser, long continuous strips, full or partial reels, tubes or trays. We machine place from all of those types of packages. What’s important is clear labeling and organization.
Individual, or mixed/loose components are not good, though. Pins get bent, leads get contaminated, values get mixed… Leave them in the strip, even if it’s short. If you’ve got multiple short strips of the same part, we can still machine place. Don’t tape them together. We can deal with them as is.
Peter Piper Picked a Peck of Pickeled Manufacturing
It’s late. Do you know where your printed circuit boards are? Let me rephrase that: Can unused PCBs be stored for future use?
Yes, they can – if stored properly. Keep them wrapped up, or sealed in a bag. Anti-static isn’t necessary in this case, but it won’t hurt. Keep them in a cool, dark place. Keep them clean. Do your best to avoid dropping them on the floor and stepping on them.
The board in this photo was left out on a desk for a while, and then shoved into a desk drawer. The environment took its toll on the immersion sliver finish, making it very much unusable.
What can go wrong:
1. Fingerprints. The oils on your finger can etch fingerprints into ENIG or immersion silver board surfaces. If you plan on committing a crime go ahead and do this so we can catch you. If you aren’t going to start a life of crime be careful to not get your fingerprints on the board surface. Handle on the edges, or at least, don’t touch any exposed metal.
2. Moisture. Moisture is good for your skin but not for your PCBs. Over time, PCBs can absorb moisture, especially in a humid location, or the ocean. If thrown into a reflow oven they then might laminate. Store boards in a dry environment. If stored for a long time, you may want to pre-bake them prior to use.
3. Atmosphere. Sometimes dirty air can contribute to tarnish or corrosion on the exposed land pads. Dust can settle onto the boards as well. Tarnish and dust can usually be cleaned off, but corrosion can’t. Wrap up your boards for long-term storage.
Treat your boards well and you can likely use them at a later date. Don’t treat them well and you may need to replace them, wasting a bunch of money. Often, the damage isn’t as clear as in the above photo, but could still lead to poor solderability.
Don’t surf on your silver