25 Jan Surface-Mount Connector Issues
Dynamic EMS Tackles the Subject of
Surface-Mount Connector Issues
By Lewis Adie, Engineer Manager
In this series of blogs, we look at some of the questions that are often asked by customers, dispel some of the myths about the electronics manufacturing industry, and provide examples of how experienced staff can resolve issues in manufacturing.
This article will look at surface-mount (SMT) connectors, and some of the problems they can introduce for a manufacture. It will also provide a short case study of how one real-world issue was resolved.
Connectors are widely used in electronics and come in all shapes and sizes. Because of that irregularity, they normally require special placement nozzles. Further, due to their poor centre of gravity and uneven surface, tapes are often fitted to some connectors for placement. Surface-mount (SMT) connectors introduce even more challenges for the manufacturer.
Connectors are essential to connect board-to-board, system-to-system, or component-to-board. Potentially, the most widely used connectors at this time are for the USB standard and the HDMI standard. USB connectors are mainly used for charging consumer goods and connecting peripherals, and therefore take a lot of rough handling from plugging and unplugging throughout the day. That process is not always carefully performed. The need to cope with rough handling means that the connectors have to be robustly attached to the board. This is usually achieved by anchoring the connector to the board using though-hole connections, meaning that the traces are attached to the connector using surface-mount technology, and the connectors are held in place using through-hole technology.
In most cases this does not present too much of a problem for manufacturing, but when it does it can be a major headache. These types of faults tend to be batch related, so many failures come at once.
As mentioned above, SMT connectors, like USB and HDMI, are usually a marriage of two separate component types – surface mount and through-hole. These two types of technology are fabricated completely differently, and that can cause their alignments to be sufficiently offset to clash and produce short circuits.
Copper features on the PCB are produced by a photomechanical process, where artwork is aligned by tooling holes over a photo sensitive film on the board. Depending on how the artwork alignment and the board alignment combine dictates the direction of the tolerance. Of course, the pattern alignment can vary from board manufacturer to manufacturer, and even batch to batch within the same manufacturer.
Placement machines align the connectors with using fiducials as a reference, and the placement accuracy varies by machine by up to 75μm. Drill alignment also has many variables. Whilst drilling uses the same tooling holes as the copper features, the process is completely different. Drilling is very much like a placement machine, in that it aligns the drill location to the tooling holes, much like the alignment to fiducials used for component placement. The boards are stacked for drilling and like placement machines each drill size has its own location tolerance due to drill alignment.
Drilled holes can be offset in any direction, and drill-to-drill drift may also vary. Copper features can also be offset in any direction. Any tolerance build-up, combined with the component placement alignment tolerances can interfere with the connector leads as they enter the hole, causing the connector to jump out of alignment.
Even a 1o rotation of the connector body can cause the leads to short. Poor insertion alignment can also result in gap reduction due to the rotated leads across the pads – creating the correct conditions for a short circuit. Of course, with full tolerance mismatches of the drilled hole drifting one way, and the copper features in the other direction, shorts are inevitable. However, these tolerances build ups are not common and vary in severity from batch to batch and between suppliers.
Case Study of an HDMI Connector Failure
On one occasion, Dynamic EMS was working on a design using an SMD HDMI connector for a customer, which produced a lot of faults. To try to resolve the situation, the engineers at Dynamic EMS tried aligning the component with the drilled hole tolerance drift by adjusting the placement machine to accommodate the drift direction. It was a short-term fix, and in the longer term, the company would have increased the hole size.
Although the short-term fix should have solved that problem, a further batch of boards were also found with short circuits on the connector. When the Dynamic EMS engineers looked for the problem, they found that the ho
le to copper alignment was excellent. However, upon further investigation, they discovered that some boards had nodules in the left-hand side of the hole. The nodules misaligned the HDMI connector body to one side, producing a slight rotation shorting the pins. The component placement was then offset to the side to resolve the issue.
About Dynamic EMS
EMS, we understand that no two-electronic equipment manufacturing customers are the same. Their products, their supply chains, and their markets all differ, which is why Dynamic EMS offers tailor-made, customised electronics manufacturing services to customers with complex, highly diversified business.
From design to distribution, we enable our customers to be more competitive by bringing innovative solutions to market faster, with a commitment to quality in everything we do. Dynamic EMS – Your Product Solutions Architect.
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