Smaller and faster - the challenges of interconnection

3rd May 2019
Anna Flockett

Designing electronic devices is never easy, as engineering professionals know only too well. Meeting the ambitious project goals almost always means making trade-offs of some description, so as to deal with the conflicting objectives of marketing departments and end customers - who inevitably expect significantly more functionality than the previous generation, while occupying much less board real estate.

Guest blog written by Mark Patrick, Mouser Electronics.

Along with the increasing space constraints, comes a need for greater bandwidth. Modern devices are set elevated operating speed benchmarks. Also sophisticated machine vision and human machine interface (HMI) systems are becoming increasingly prevalent, and pixel counts are rising accordingly.

In order to use available space more effectively, many products now include multi-board solutions so that that things can be tackled volumetrically, as well as improving thermal management by orienting components that need to dissipate heat into the airflow. This approach also allows the integration of third-party solutions, such as communications interfaces, as well as providing scope for optional features to be added during the manufacturing process or post-sale via a dealer network.

The entire electronics industry has invested wholesale into miniaturisation - in a quest to deliver more, while taking up less space. It has focussed its combined resources on developing technologies with ever-reducing geometries, alongside innovative packaging solutions. Highly integrated semiconductors now include microcontrollers and peripheral devices in package formats measuring just a few millimetres square. At their smallest size, passive components - such as chip resistors - are more akin to specks of dust than items of electronics.

In the world of connectors, manufacturers have been challenged to respond to these needs and to keep pace with industry-wide miniaturisation efforts. Twenty years ago, the most common pitch for connectors was 2.54mm while today connectors with pitches as narrow as 0.35mm are available. Delivering these geometries in FPC connectors has pushed stamping and moulding procedures to their limits, while driving flex-circuit vendors to implement tighter tolerances for mating mechanisms.

Even in the realm of board-to-board connectors that are essential for modern high-density designs, geometries have reduced significantly, reaching down to 0.4mm pitch. However, in order to achieve the tight spacing required in modern designs, boards must be stacked close together, meaning that the height of these connectors has also been squeezed, with solutions available as low as 2.0mm.

Molex 202828 Mirror Mezz connectors are footprint-compatible hermaphroditic units that offer stackable mating, thereby delivering markedly lower installation costs. These connectors support data speeds of up to 56Gbps per differential pair - making them highly optimised for telecommunications and networking applications. The Mirror Mezz connectors feature an innovative stitched ball-grid-array (BGA) design and benefit from an intricate terminal structure with industry-leading mechanical strength, as well as the most cutting-edge electrical features. Typical uses include servers and data storage.

TE Connectivity's 0.8mm pitch free height board-to-board stacking connectors allow designers to achieve a wide variety of stacking heights (from 5mm to 20mm, in 1mm steps) between PCBs without having to make changes to their PCB layouts. These stacking connectors offer 40 to 200 positions, 0.8A per pin current ratings and operating speeds of up to 10Gbps. There are a variety of plating options available, allowing designers to select components in respect to specific performance and cost parameters. Typical applications here include mobile point of sales (PoS) equipment, outdoor LED displays, automotive and home entertainment/home security.

In situations where cost is a primary consideration, Amphenol FCI’s BergStak Lite 0.8mm double-row pitch components offer high-density connectivity at economical price points. The parallel board-to-board connectors are available in 40, 60, 80 or 100 positions. They can be supplied in 16 PCB stack heights (from 5-20mm, in 1mm increments, as with the products from TE Connectivity). The scoop-proof housing and terminal profile enable support for data rates up to 12Gbps and the gold flash contact plating can cope comfortably with 50 mating cycles.

In tough environments, rugged solutions are needed to ensure long-term interconnection integrity. Released back in the spring, Harwin’s Archer Kontrol board-to-board offering is capable of delivering increased reliability, with each unit being rated for a minimum of 500 cycles. These robust and flexible 1.2A-rated, 1.27mm connectors are available in horizontal and vertical orientations, with between 12 and 80 contacts. Different height options for vertical models are also available in both male and female styles. The fully shrouded and polarised connectors are very well suited to blind mating and can withstand lateral and twisting forces, as well as heavy vibrations. Consequently, they are of value in industrial, handheld, IoT and transportation contexts.

Figure 1: Harwin Archer Kontrol.

One of the lowest profile connector series currently available is Hirose Electric’s BM28 board-to-board/board-to-FPC offering - where units have a rated current up to 5A and a 10Gbps data carrying capability. Both the power and signal contacts are gold-plated, copper alloy and feature a two-point contact design. The guide ribs ensure 0.3mm self-alignment and create a tactile ‘click’ for added mating confidence, giving the BM28 series superior reliability and operability. These halogen-free connectors have a 0.35mm contact pitch and 0.6mm stacking height, saving significant overall space. The BM28 series makes use of straight SMT type terminations and features models with both receptacle and header connector types, ranging from 6-60 signal contacts. These connectors are targeted at modern space-constrained deployments - such as wearable technology, smartphones and tablet PCs.

Clearly, the connector industry has successfully responded to the needs of today’s under-pressure design engineers. It has delivered a wide range of innovative solutions that offer rugged and reliable high-speed operation in smaller form factors, even when there are harsh environments to contend with.

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