Case Study: Factors in Connectors for PEMS Applications

Phil Heft, Business Development Manager - North America, Memcon

Phil Heft, Business
Development Manager
- North America,
Memcon

Considerations for your membrane switch design involve how to connect the circuitry with the brains that control your product. Basically, membrane switch connectors join together the keypad and the device it will control. Connectors consist of a contact device and a molded plastic housing, but membrane switch connectors are certainly not something to choose lightly. Sometimes, knowing which connector to use for an application can be difficult. You need to think about ways to accommodate connector durability and minimize unwanted space when deciding how to terminate your membrane switch.

Flexible membrane switches are connected by a flexible tail that is cut from the circuit material. This flexible tail can be connected to a circuit board header, an extender jumper cable or even discrete wire with a variety of single row connectors designed for flex circuits. As another option, the tail can be designed to interface with a zero insertion force (ZIF) or low insertion force (LIF) connector. Typically, the lowest-cost interconnect is a ZIF or LIF connector, though it is fragile in design and difficult for printers to hold tolerances for effective use.

Discrete wire mating to flex cable with latching style

Discrete wire mating to flex cable with latching style

Circuits may also be terminated with solder tabs that can be directly soldered onto the circuit board. They have been proven to work well in industry environments with heavy shock or vibration, though soldering to printed circuit boards (PCBs) can be tricky and not repairable. Solder tabs are approximately $0.015 per position.

Both male and female crimp connectors are considered to be reliable against heavy shock and vibration allowing ease of assembly and repairs. Male or female connectors have pins crimped to the circuit and are available with many different housing features.

The tail pitch is available at .100- or .050-inch spacing with a selection of variables to accommodate applications.

When selecting a connector for your PEMS switch, a number of factors should be considered, including cost, reliability, performance, design, environment as well as any anticipated insertions and extractions. Mechanical specifications for most interface terminations are industry standard so design is made for compatibility with specific types of mates (PCB or cable).

Latching 1.27-millimeter housing MH545

Latching 1.27-millimeter housing MH545

Crimp type connectors provide a gas-tight termination interface between tail and contacts (male/female or solder tab) with or without housings. Connector costs will depend on contact plating material (tin or gold), the number of pins required as well as connector pitch. With more sophisticated circuit designs — including embedded components — higher pin counts are becoming more common where .050-inch pitch connectors are used. Though this does save a great deal of space, it does come at higher costs.

The determination of plating should be among the first considerations. Though tin is well received and represents the highest percentage of contacts used in the industry, gold is more durable and has a more lubrous attribute. Gold should be considered when designing for higher than 50 insertion/extractions (rated to 500). It should also be considered for higher pin counts. Typical tin pricing is like the solder tabs at about $0.015 per position and gold is typically $0.03 per position.

Female contacts at 0.100 inches also can offer insertion/extraction specifications — high insertion (MHFC025) styles are typical for eight or fewer pins, a low insertion force (MLFC506) for higher pin counts. In recent years a third style designated as hi-flex presents a best option across the spectrum of design. The Hi-Flex (MHFFC106) presents a tweezer tip spring design that works in all pin counts and has the added benefit of surviving intact from damage of bent male pins or operator rocking of the connector for extraction. All variants crimp identically on machines and work with all plastic housings and all styles maintain comparable pricing.

MHD Detent Style Housing with mating male headerConsiderations for plastic housings that complete the connectors add features that ensure proper mating or secure them from vibration or inadvertent pulling of tail. The most common housing (MHF Series) creates an unpolarized, non-locking connector. It carries the least cost but without mechanical features. Should you need to polarize, a simple plug (MKP101) can be placed in any position of the connector, blocking a hole to ensure proper direction of the mating to simple male pin headers.

MHD Detent Style Housing mating male header

MHD detent style housing with mating male header

A housing series was created to provide polarization. This MHP Series has vertical fin tabs that mechanically will only mate when properly orientated.

If you prefer a latching series which will effectively polarize and secure the connection, use the MHJ style. There are additional options made specifically for mating to Tyco (MHL) or Molex (MHM), but the MHJ is universal and carries no additional cost. It also features guards to prevent the latch from getting caught in stray tails and potentially tearing off.

A detent feature offered by the MHD Series provides some strain relief in the mechanical mating to its proper header. Though it won’t prevent detachment, the detent can help secure in high vibration or inadvertent pulling of the tail.

Should you require a full locking system — a system in which you will not be able to remove the connector from the header without a tool (such as a screwdriver) — consider the MHE Series. The plastic has a horizontal ridge, which, when engaged with the proper male header, will fit into its molded profile. To disengage requires flexing the wall of the header outward, freeing the ridge from the wall.

All plastic housings come at the same or similar pricing, typically between $0.015–0.02 per pin position. So, for a typical connector in any style, anticipate total costs from $0.03–0.035 per position in tin (i.e. a 10 position connector would be ~$0.30 total) and $0.045–0.05 per position in gold (i.e. a 10 position gold version would be ~$0.50).

An alternative integrated connector series (MICC801) is also common. Though the end result of the completed connector on your tail is the same industry standard created by the two-part connector series with the MHF housing, this system is complete with contacts already in the housings. The system is popular with companies without benchtop crimping machines as it is able to be crimped on tails with a hand tool (though a benchtop unit is also available). This allows field repairs or installations easy to accomplish. The cost per connector position will run two to three times the cost of the two-part system.

The crimping method for the integrated connector is a bit different and in certain designs may be preferable. The contact tines are clamshell style (top and bottom) and when ink traces are on both top and bottom — scalloped tails, for example — it is a more natural environment for this style. You can address these designs with the two-part connectors but may require some engineering.

Male pin crimp connectors are also available. As opposed to male solder tabs that are stamped flat, male contacts for connectors are formed with depth to mate to female connectors. The crimp tines are identical to the female style but may require specific tooling due to length differences. The short male pin contact MSSMC595 is designed to not need a plastic housing and offers an inexpensive solution. (Note: Without a plastic housing, the crimp area is exposed and not insulated, so a suggestion could be taping.) The standard male pin MSMC410 does need a plastic housing to complete. The standard MHF series, however, will finish the connector without polarization or features. Should you design to mate to the latching female connector, use the MH1L housing.

Custom styles can easily be created — whether a simple color variant, using block pins instead of polarizing plugs, accommodation of design for thicker materials or any design you would like to discuss — mold changes may prove to be less costly than redesign.

The .050-inch pitch connectors offer less options, but the most common are standard or latching and single or double row. These varieties are commonly stocked items. Contact variations consist of male solder tabs (standard MFPMC923), short male solder tabs (MFPSMC940) or female (MFPFC547) in gold or tin. Housings are available as unlatched (MH544) or latching (MH545). Double row versions of both are standard as well. The 1.27-millimeter system costs per pin counts are nearly three times the 2.54-millimeter system, so comparable to the integrated pricing.

Memcon, a global supplier to the membrane switch and flexible technology industry, is a solution provider for all crimp connectors as well as a worldwide supplier and resource to PEMS. They manufacture contacts, housings and integrated connectors, along with crimping equipment. Mating headers are also available along with a full range of products and services to the PEMS community.

Electronica Munich 2018
Printed Electronics USA

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