Custom interconnect solution provides space savings

Although the term ‘PCB’ tends to elicit the image of a solid, green, rectangular circuit board covered in traces, today’s advanced electronics frequently employ PCBs with cut-outs in a variety of shapes and sizes to enable reduced-size end devices. The geometric mismatch between irregularly shaped PCBs and standard rectangular connectors, and especially those with lead-frame contacts, can make it extremely difficult to impossible to make efficient use of limited PCB real estate and achieve the high component density.

Connectors are widely available in a multitude of shapes and sizes, but the unique size, weight and performance demands of many new, next-generation electronics require customised solutions to meet those specifications both on budget and on time, and especially when the solution must also meet stringent standards.

As a case in point, a customer had a request for a small, lightweight and low-profile surface-mount connector that would maximise real estate on a uniquely shaped PCB and meet the rigorous performance and long-term reliability demands of a mission-critical application. They also requested keying and polarisation capabilities to facilitate blind mating, minimal tooling and set-up costs, and a quick turnaround time. Their request was brought to Advanced Interconnects, a leading designer and manufacturer of innovative, technologically advanced interconnect solutions.

To fulfil the request, design engineers at Advanced Interconnects literally thought outside of the box, bypassing traditional rectangular configurations in favour of a semicircular configuration capable of utilising the perimeter of the PCB, providing both the ruggedness and flexibility required, and achieving a low, 6 mm stack height. Board-to-board connectors that utilise screw-machined terminals with multi-finger contacts are ideal for meeting the high-reliability demands and design requirements. And these designs are typically custom-made using high-temperature moulded, FR-4 or polyimide film insulators with application-specific features such as shrouds, standoffs or special plating.

To achieve the necessary reliability and overall size reductions, the team employed a 1 mm-pitch ball grid array socket adapter contact system with a solder ball PCB interface. This contact system’s screw-machined terminals have multi-finger contacts that are said to provide superior reliability and performance over stamped-and-formed pins and can accommodate a variety of low-voltage differential signalling (LVOS) requirements for power, signal and ground options. The proprietary solder ball terminal design provides a strong solder joint with enhanced elasticity, effectively compensates for minor co-planarity issues between boards, and is said to take up less space than typical lead-frame technology (eg, lead-to-trace or PCB pad).

The team then employed customisable FR-4 insulators, which eliminate tooling costs since they don’t require a mould and allow for multiple design revisions and fast prototypes during the development phase, along with fine-pitch BGA socket adapter terminals, which are available in pitches down to 0.5 mm.

Once the design was complete, the engineers used precise CNC machinery to create rough samples for electrical and mechanical testing, achieving a fast, custom request to ready-to-test prototype span of less than five days. Created from FR-4 on an in-house driller/router machine, the prototype connector incorporated 1 mm-pitch solder ball terminals on both the male header and the mating female socket and alignment pins for a fully keyed and polarised solution that could facilitate blind mating. Vertical integration and existing screw-machined terminal designs eliminated the need for expensive tooling and set-up costs, such as stamping dies, which made the custom solution a quick and affordable way to satisfy a range of application requirements.

By leveraging in-house engineering expertise, field-proven interconnect technology and precision machinery, the following six key specifications for the custom 70-position SMT Perimeter Connector application were being satisfied: mission-critical reliability; maximised real estate on a rounded PCB; keying and polarisation capabilities; lightweight, low-profile form factor; minimal tooling and set-up costs; and quick turnaround time.

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