Interconnection


Developments in connector technology to mitigate


misalignment By Ryan Smart, VP of product, Harwin H


igh-volume manufacture using automated pick-and- place machinery has become commonplace in a growing number of electronics applications.


However, such techniques can present a challenge to OEMs when it comes to the successful, reliable and repeatable mating of board-to-board connectors during the manufacturing process. What’s more, this challenge increases in complexity with increases in the number of fine-pitch connectors per board that need to be successfully mated on an automated production line.


Board-to-board connectivity A mezzanine card, or daughter board, can provide a convenient way for engineers to achieve specific design goals. Stacking one board above another can help make best use of available space within the enclosure, simplify the design of the main PCB, allow customizing hardware for a particular market, or enhance repairability.


Among the options for passing signals between the two assemblies, a board-to-board connector can allow fast mating and reliability, ensuring mechanically robust and correct connections every time. There are many options to choose from including low-profile connectors that allow close spacing if low overall height is a priority, or taller connectors to provide clearance for components on the main board or to allow airflow.


A single connector can simplify design and the two boards are easily mated during product manufacture. However, if the main board contains too many components or not enough layers to allow all the necessary signals to be routed through a single connector, two or more connectors may be needed. Alternatively, signal integrity issues may dictate the use of two connectors to separate digital signals from


44 June 2024 Components in Electronics www.cieonline.co.uk


Figure 1. Highly accurate positioning is needed when mating two or more board-to-board connectors


analogue, or ensure differential signals are optimally arranged.


Placement accuracy


If more than one connector is needed, mating becomes more challenging as both parts of each connector need to be properly aligned when the boards are brought together (figure 1). The connectors are often small, with sub-millimetre contact pitch, and – for efficiency and accuracy – assembled as part of the same automated processes used to populate the boards with surface- mount electronic components. Although high-speed inline placement systems are extremely accurate, small errors can accumulate. The datasheet for a top


machine may state positional accuracy of ±0.035 mm. Similarly, screen printers can deposit solder paste within ±0.08 mm. Moreover, manufacturing tolerances in PCB fabrication can affect the pad positions, and there is potential for parts to move during soldering.


Worst-case errors accumulated across the four mating halves of two separate connectors could be enough for connector housings and soldered joints to experience stresses when the connectors are mated. These can cause problems such as poor electrical contact and fracturing of the connector body or soldered joint, causing failure of the unit at end of line test or in the field.


Figure 2: Floating connectors do not require absolute alignment


Connectors accommodate alignment tolerance


Among the options for overcoming these effects and ensuring accurately aligned mating free from potentially harmful mechanical stress is the ‘floating’ connector. By allowing x, y, and z movement of one set of contacts, these can accommodate misalignment and hence reduce reliance on absolute positional accuracy when mating boards that contain multiple connectors.


As an example, Harwin ‘Flecto’ - a range of fine-pitch board-to-board connectors that provide a high pin count, with up to 160 connectors in a symmetrical double-row layout - incorporates a floating sub-assembly design that lets the male connectors move by


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60