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Vol.01 A revolution in board interconnect creates new value

Electronic equipment uses an enormous quantity of contacts and connectors to interconnect boards, modules, and components. If you’re an equipment design or production technology engineer working with these contacts and connectors, take a look at The Spring Contact (micro clip) low-profile spring contact developed by Alps Electric. It can replace conventional spring contacts and connectors to resolve a host of problems, and facilitate development of equipment you thought impossible. The Spring Contact (micro clip) is technological evolution in a part of the equipment you thought would ever change, providing smaller equipment, improved reliability, higher performance, part count reduction, and simpler manufacturing processes all in one. Your imagination is the only limit on its enormous potential.

The Spring Contact (micro clip) is a new spring contact technology (Fig. 1) based on the precision pressing technology of Alps Electric. The contact package is extremely small, but maintains stable contact performance even when subjected to vibration or impact, from any angle.

Fig. 1 Micro clip spring contact, now in volume production by Alps Electric

Consumers will never see the part, and they will never directly feel the effect it provides in consumer products, but even so The Spring Contact (micro clip) will have a huge impact on electronic equipment design and production technology development. Consumer electronics, industrial equipment, office automation—The Spring Contact (micro clip) could replace all of the countless contacts and connectors used in electronic equipment in every field.

Master connectors, and you master the equipment business

In order to continue providing electronic equipment that offers higher performance and reliability in a smaller size, it is essential to concentrate as many function s as possible into one board, or one chip. Board interconnect remains vital, though, because there are a variety of reasons why the one-board, one-chip design method is avoided: it may be necessary to separate the verified modules from the one that is still undergoing rework just before market release, or a separate board may be needed to prevent company technology from being released to contractors, or perhaps boards made in different nations are assembled elsewhere. Advances in interconnect technology between boards, modules, and components are essential in providing more options in the electronic equipment business.

There has been very little real progress made in technology for connections between boards, or between boards and components, however. The plugand-socket connectors and soldered cable connections of half a century ago are still being used today. In many cases, problems with connection technology have actually held back electronic equipment evolution.

Connector socket layout can significantly affect circuit performance, but design considerations can force the connector into a board corner at times. For example, even if the engineer knows that a particular board location will minimize trace length and noise while simplifying wiring, there are often times when the connector must be on a board edge. A single connector component requires a total of five parts: the socket and plug for each connection end, and the cable between them. And in assembly, the plugs must be inserted into the sockets, for another process.

Conventional spring contacts, however, often suffer from poor reliability caused by the effects of corrosive gas, or structural problems that can cause tiny offsets in contact location and change operating characteristics.

Bringing together all of Alps Electric’s fabrication technologies

Takashi Kawahata, Group Manager, No. 3 Group (left), and Jun’ichiro Yokota, No. 2 Group, both of C5 Engineering Dept., Engineering Headquarters, Alps Electric.

“It’s a breakthrough for all those interconnect problems that engineers had given up on ever solving with existing technology,” says Takashi Kawahata (Fig. 2), Group Manager, No. 3 Group, C5 Engineering Dept., Engineering Headquarters, Alps Electric.

The Spring Contact (micro clip) is smaller than existing spring contact solutions, but offers dramatically superior reliability. With connectors, it becomes possible to locate the connection at any point on the board. The part is very small, and has a square footprint to make it even easier to optimize the connection point without seriously impacting the layout. It can interconnect boards for an effect very close to that of a multi-layer board. A single unit can be connected with just a push. Now boards can be assembled without any insertion process, and multiple connection points can be closed simultaneously. The simpler assembly process benefits to automated assembly systems, too.

The structure of The Spring Contact (micro clip) ensures its high reliability. The two spring coils allow the contact point to float freely. Once The Spring Contact (micro clip) penetrates the oxide film on the opposite contact point and makes a connection, it will not slip out of contact, maintaining a stable connection even when subjected to vibration or impact. It delivers contact reliability even with flexible boards.

Flg. 2 Distributed contact points with The Spring Contact (micro clip)

The footprint is only 1.4 mm square, helping shrink board area while improving layout freedom. Because ground can be provided anywhere on the board, circuits operate faster and with more stability than ever, and in many cases noise-suppression components can be cut to further reduce cost. “There are some pieces of equipment that cannot be produced through assembly, and this technology can be used to simplify the manufacturing processes required,” explains Jun’ichiro Yokota, No. 2 Group, C5 Engineering Dept., Engineering Headquarters, Alps Electric. Together with emerging materials, a new dimension in equipment evolution is opening up.

The Spring Contact (micro clip) will become a crucial strategic component for electronic equipment manufacturers, and already equipment design and production technology are being based on its capabilities.

Requirements for faster, smaller, and more reliable products have made the design of embedded printed wiring boards (PWB) for electronic equipment significantly more difficult in recent years. The Spring Contact (micro clip) developed by Alps Electric is designed to address these problems. We brought together experts in electronic design in a number of fields and Alps Electric engineers to discuss the applicability and potential of the micro clip. Tough questions were posed by Minatake Kasio, an expert in technology analysis who has done teardown analysis of diverse electronic equipment; Tadashi Kubodera, an authority in electromagnetic noise suppression, with experience in equipment demanding high-speed operation and high reliability; and Naoki Kunimine, an expert in thermal design. Just how did these experienced, real-world engineers evaluate The Spring Contact (micro clip) ? Find out in this two-part report.

Ito: The Spring Contact (micro clip) is a totally new concept in contacts, connecting the PWBs in electronic equipment. Structure and characteristics are quite different from existing contacts. We have brought together a group of specialists in modern electronic equipment design to probe the applicability and potential of The Spring Contact (micro clip), through discussion with the engineers who created it.

Advantages Over Existing Spring Contacts

Minatake Kashio
Director,
Fomalhaut Techno Solutions
Tadashi Kubodera
President,
System Design Lab

Kashio: If you pop open a new smartphone, you’ll see a lot of spring contacts being used to connect the antenna, battery, and other components. Just how much better is The Spring Contact (micro clip) than these existing contact technologies?

Yokota: Smartphones these days use a flat spring contact, with a thin metal sheet bent over on top of itself. It has a relatively large footprint, and while it can absorb vertical motion, the contact point can be offset by force in the horizontal direction. The Spring Contact (micro clip), on the other hand, has a unique double spiral spring structure that supports a contact point, floating it to absorb vibration and impact. This design is both smaller and much more reliable.

Kawahata: Smartphones also use probe pin-type spring contacts, with a bullet-shaped terminal combined with a coil spring in a cylindrical package. These probe pin contacts consist of the plunger, which moves vertically, and the barrel around it, and most of them are designed for very low currents. The Spring Contact (micro clip) achieves direct contact with a single part, and can handle up to 3 A with stable performance. That means it can be used with the low-profile components essential in ultra-thin smartphones and similar devices.

Kashio: As smartphones grow thinner, an increasing number of components are being mounted on flexible boards. The Spring Contact (micro clip) can be used to interconnect rigid boards to metal cases, and rigid boards to flexible boards. It has a very wide range of application that allows it to make a major contribution to achieving thinner electronics.

The Merits of Connecting Anywhere

Yoshio Tanabe
Senior Manager, Engineering Dept. C5,
Furukawa Plant,
ALPS ELECTORIC
Takashi Kawahata
Group Manager, Engineering Dept. C5, Group 3,
Furukawa Plant

Kubodera: When mounting two PWBs against each other, connectors have usually been placed along the periphery, making it necessary to route traces to the board edge. This generally lengthens the lead, and that it something that should be avoided if at all possible to minimize noise. The Spring Contact (micro clip), however, can be placed anywhere on the board, making it possible to keep board leads short, which is very exciting for a designer.

The devices that require these tiny components, though, often use very thin boards, only 0.4–0.5 mm thick. Concentrating load in a single point can easily cause warping in boards this thin.

Yokota: A dense population can cause high loading, and warp the board. I think that sort of problem can be avoided by optimizing layout in the design stage, though.

It Looks Like a Simple Inductor...

Hiroyuki Takaoka
Engineering Dept. C5, Group 3,
Furukawa Plant
Junichiro Yokota
Engineering Dept. C5, Group 2,
Furukawa Plant

Kubodera: The spiral structure of the micro clip makes it look like a coil inductor. How high a frequency can it handle?

Takaoka: As far as self-resonance goes, it can handle signals above 6GHz, with the inductance component suppressed to 1 nH.

Kubodera: From bottom to top, then. That value’s as low as a single through-hole.

Takaoka: That’s right. The spiral carrying the current has two signal lines running in parallel, delivering outstanding frequency characteristics.

Kubodera: When it’s being used as a transmission path for a high-speed signal, you have to use one line for the signal and the other for the ground.

Takaoka: For high-speed signals, we think the best approach is to use a set of three, carrying ground, signal, and ground again.

Kubodera: Wouldn’t the characteristic impedance change depending on the distance between the micro clips? There isn’t any dielectric with stable characteristics between the signal and the ground, like the board. And that would make it impossible to calculate the characteristic impedance, I think.

Takaoka: True, the distance between signal and ground will affect the characteristic impedance. When we evaluated this point using time-domain reflectometry (TDR), the length of the signal path in The Spring Contact (micro clip) was so short it was very difficult to determine the characteristic impedance. The results indicate that for a practical separation, it should be enough to just verify a good eye pattern to be confident of handling a high-speed differential signal.

Kubodera: If users can verify that reflection isn’t a problem, I think this is going to be picked up very quickly by the industry.

Superlative Reliability

Kubodera: Depending on the surface roughness of the board it presses against, contact performance of conventional spring contacts can change over time. There’s no worry of that happening here?

Ito: Mr. Naoki Kunimine, experienced in thermal design, also asked about reliability. He said that Joule heating from contact resistance at the contact point tends to increase over time, and wanted to know if The Spring Contact (micro clip) has been designed to extend service life in this regard.

Tanabe: In conventional spring contacts, the contact point can shift with vibration, magnifying the effects of surface roughness and contamination and causing characteristics to change over time. Another cause of change in contact resistance over time is the oxide film forming on the contact surface when it moves, or floats, and comes into contact with air. The Spring Contact (micro clip) has a floating structure that absorbs vibration and impact, preventing motion at the contact point. It won’t move once it’s connected. And that means that even if the surface gets a little contaminated, or is subjected to vibration or heat, the connection remains stable.

    Eye pattern simulation (5 Gbps differential signal)

The Era Demands Resilience to Vibration

Kashio: Strong resistance to vibration and impact would make it useful on control boards for drones. They generate quite a bit of vibration in flight, and circuit breaks are a constant worry even with soldered bonds. That makes it impossible to design circuits with a large number of bonds. Drones demand very high in-service ratios, and generally use a single board even when it represents a cost increase. Drone developers are already searching for high-reliability board-to-board interconnect technologies, and if contact point offset is eliminated, that’s a major development.

Tanabe: The features of The Spring Contact (micro clip) make it perfect for that type of application. Soldered and other fixed bonds can be destroyed by stress.

Ito: We will see more and more equipment designed for very active motion, or for use in harsh environments, like robots and wearable terminals. Applications like these may represent a new market for The Spring Contact (micro clip).

Support for taller components

Ito: Our discussion has already confirmed that The Spring Contact (micro clip) has the potential to make PWBs faster, smaller, and more reliable, but it is extremely unlikely that The Spring Contact (micro clip) will immediately replace every contact and connector in use today. I’d like to turn the discussion toward an examination of future evolution for the technology.

Kubodera: The Spring Contact (micro clip) on the market now have component heights of 1.2 mm, and mounted heights of 0.7 mm, defining the gap between two PWBs connected together with The Spring Contact (micro clip). This is pretty tight, and limits the electronic devices that can be mounted. I think the potential of the micro clip can only be fully realized if it can handle taller components, too.

Kawahata: We are now developing a range of mounted heights. We started off with the 1.2-mm design deliberately, because we were targeting products like smartphones that place a high premium on thin, small, and light designs. We wanted to make the advantages of The Spring Contact (micro clip) really stand out. We have already received requests from our customers to make The Spring Contact (micro clip) capable of handling 5- or 6-mm components, though, and if there’s sufficient demand we’ll manufacture them.

Continued pursuit of even smaller designs

Kubodera: At present, The Spring Contact (micro clip) is only available in a 1.4-mm square design, but we are working on a model that will be no more than 1 mm on a side. That will make it possible put a contact between two PWBs anywhere, such as on a ground. Designers need the ground potential of the two boards to be as close to each other as possible, to minimize noise, and often want to put a connector in a very tight spot. If we can make The Spring Contact (micro clip) that small it will significantly increase design freedom. This type of application is perfect for The Spring Contact (micro clip).

Tanabe: This miniaturization is, of course, one direction of evolution. The value of The Spring Contact (micro clip) is a result of its unique structure, which absorbs impact and vibration to deliver highly reliable contacts. The structure consists of two spiral springs that maintain a 3D, floating contact position. Any miniaturization must preserve this performance. We’ve verified the performance of the 1.4-mm square design, and we believe that the even-smaller design will be applicable to almost all board interconnect applications.

High-frequency performance for expanded design freedom

Kubodera: Can high-frequency signals be run through The Spring Contact (micro clip) ? For example, mutual interface between circuits operating in the same waveband can cause misoperation in wireless local area network (LAN) and Universal Serial Bus (USB) applications. One very simple countermeasure is just to physically separate the circuit causing the problem. These days, however, many chips are using pretty high frequencies internally, and often these high-frequency signals are transmitted between boards. In personal computers, for example, a single PWB might mount the central processing unit (CPU), memory, input/output (I/O), and audio circuits, and interference between them is a lot more likely. If boards could be more easily separated from each other it would expand design freedom.

Ito: What would be the benefits of being able to pass high-frequency signals between boards?

Kubodera: Separating boards from each other sounds like it would increase cost, but trying to put everything on a single PWB often means having to switch to a multi-layer board. Just separating the boards from each other can be a lot cheaper. The connectors that always cause so much trouble in hybrid integrated circuits (IC) and multi-chip modules (MCM) are no longer needed with The Spring Contact (micro clip), which is just frosting on the cake. But in order to make it happen, it has to be possible to swap high-frequency signals between boards, which is why I’m curious if it’s possible or not.

Tanabe: There are already ultra-fine co-ax connectors that can handle high-frequency signals, but they have various issues as far as reliability, size, and ease of use. With small size and outstanding design freedom, The Spring Contact (micro clip) should be able to handle high-frequency signals with good signal and ground design.

Waterproofing and other features

Kashio: How many pins do you have in mind when you talk about using the micro clip to interconnect two boards? The flexible boards in new smartphones, such as for near-field communication (NFC) circuits, use 9-pin contacts. I think that’s a good example of one of the highest pin counts for a commonly used connector.

“The features of the micro clip make it very effective in a wide range of applications.” (Kubodera)

Tanabe: The current design should be able to handle up to 10 pins. In addition to interconnecting two boards, we’ve also thought of using it in smartphones with waterproofing, for example. In waterproofed electronic equipment it is impossible to solder the earphone jack to the PWB, and run it out through the case. The jack and connector have to be mounted on the case, and connected to the board via a flexible connector, because the case connector cannot be soldered to the board. A micro clip would vastly simplify this construction.

Kubodera: The ball grid array (BGA) is currently the leading semiconductor package, but it is impossible to tell where a contact fault has occurred once it’s mounted. If the balls are replaced by The Spring Contact (micro clip) it is trivial to attach and detach the connector, providing a major improvement in efficiency in prototyping. The same applies to all removable components, of course, not just BGA.

Tanabe: Micro clip arrays will be necessary for it to handle high pin counts, or replace BGAs. The Spring Contact (micro clip) is square, however, making it ideal for arrays.

Handling high currents and thermal radiation

Kashio: Apple Corp of the US uses a USB3.1 Type C connector, with a maximum capacity of 5 A, for the charging port on its MacBook notebook. The current iPhone model uses a 3-A Lightning connector, but is expected to switch over to the same Type C used in the MacBook. Higher currents make possible convenient rapid charging, and will no doubt be a key development item from now on. Can micro clips be used to connect the battery to the board, for example, with these high currents?

Kawahata: The current design is rated to 3 A, but we believe that the trend is toward higher amperages.

Ito: Mr. Naoki Kunimine, the thermal management specialist, wants to know how much the temprature increases when it’s conducting 3 amps.

“Many smartphones on the market today can make good use of the features of the micro clip.” (Kashio)

Takaoka: In-house tests showed 15°C. We believe that this is an acceptable level.

Ito: Another question is whether high-temperature creep can cause failure if contact load is applied in the high-temperature state.

Yokota: We have implemented design measures to ensure that the temperature does not reach that level, and selected heat-resistant materials.

Tanabe: I wonder if The Spring Contact (micro clip) couldn’t be used to get rid of excess heat, instead of just for electrical connection. Even with heat sinks it can be difficult to radiate the heat generated by semiconductors and electronic components. A row of micro clips would function as a thermal radiation path.

Advanced manufacturing technology makes volume production possible

Kashio: The development team has made it clear that there is some major change on the horizon in contacts and connectors. I think I’ll be running into micro clips in a lot of the electronic equipment I take apart in the future.

Kubodera: The features of the micro clip make it very effective in a wide range of applications. I’d guess dropping the cost is the key to widespread market adoption.

Tanabe: The Spring Contact (micro clip) can be manufactured by pressing from a single sheet, and it is not as expensive as it might look, considering its visual complexity. Still, sophisticated manufacturing technology is necessary to maintain the necessary precision in repeated production cycles. Fortunately, that’s something Alps Electric is very good at.

Ito: The current micro clip is not the mature design. We realize the technology will continue to evolve, leading to a diverse selection of new types. We are confident that it will grow into a major new technology that can help electronic equipment designers resolve the many issues they face today.

【Major characteristics】

●The Spring Contact (micro clip) ultra-miniature spring contact, with the smallest footprint in the world
1. Low profile, small footprint 1.4 mm square
2. Unique spring structure ensures high contact reliability even when subjected to vibration or impact
3. Square shape eliminates mounting directionality for layout flexibility
4. Small size can still handle currents up to 3A
5. Can be handled by standard-nozzle chip mounters

【Major applications】
Personal audio Cameras
Health care PC & peripherals
Mobile phone & peripherals Wearables electronics
Car AV equipment  
【Major specifications】
Product nameThe Spring Contact (micro clip)
External dimensions(W×D)1.4mm×1.4mm
Mounted height0.7mm to 1.0mm
(inquire for other heights)
Rated current3A
Operating temperature-30 to +85℃