Strategies for High-Density PCBs

As hand-held and portable electronic products and their circuit boards continue to shrink in size, the designer is faced with solving the physical differences between traditional printed board fabrication and what’s commonly referred to as high-density interconnect (HDI) processing. The primary driver for HDI is the increased complexity of the more advanced semiconductor package technology. These differences can be greater than one order of magnitude in interconnection density.

Semiconductor Packaging

Although the development of array-configured packaging for ICs has alleviated circuit routing difficulty somewhat, product miniaturization and performance goals are not easily achieved. To further complicate the PCB design process, many companies furnishing multiple die or multi-functional semiconductor packaging are forced to significantly increasing I/O while reducing both contact size and pitch. This higher I/O and finer pitch evolution is due in part to the OEM need for more capability in an ever-shrinking space. Further complicating traditional PCB design, some companies are doing away with some or all traditional semiconductor packaged semiconductors.

System-in-package (SiP) for example, whether die stack or package-on-package, has rapidly penetrated most major market segments. This includes consumer electronics, mobile, automotive, computing, networking, communications, and medical electronics. The benefits of SiP will differ for various market segments but they can share some very common elements: shorter time to market, smaller size and lower cost. Area efficiency (more functionality in a single package footprint) has resulted in the strongest initial penetration in consumer electronics. These mixed function SiP solutions have become commonplace in small form factor systems, such as mobile phones, memory cards, and other portable electronics products and the number has been increasing rapidly.

In contrast, it has become common for developers to procure bare, uncased die elements that are configured for facedown (flipchip) mounting. Although flip-chip was originally considered for relatively low I/O die, the redistribution of the peripheral located contact sites to a more uniform area array format has enabled the commercial use of larger and much higher I/O die elements. Regarding flipchip mounting, interconnection from die element to the PCB is commonly achieved with alloy bumps, spheres or, for very fine pitch applications, raised copper pillar contacts that, although very small, are compatible with a conventional reflow soldering processes.

To read the full version of this article which appeared in the November 2017 issue of The PCB Magazine, click here.

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2017

Strategies for High-Density PCBs

11-27-2017

As hand-held and portable electronic products and their circuit boards continue to shrink in size, the designer is faced with solving the physical differences between traditional printed board fabrication and what’s commonly referred to as high-density interconnect (HDI) processing.

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2016

Specifying Lead-Free Compatible Surface Finish and Coating for Solderability and Surface Protection

07-06-2016

A majority of the components furnished for electronic assembly are designed for solder attachment to metalized land patterns specifically designed for each device type. Providing a solder process-compatible surface finish on these land patterns is vital...

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Flexible and Rigid-Flex Circuit Design Principles, Part 6

05-26-2016

The designer is generally under pressure to release the documentation and get the flexible circuit into production. There is, however, a great deal at risk. Setting up for medium-to-high volume manufacturing requires significant physical and monetary resources. To avoid potential heat from management, the designer must insist on prototyping the product and a thorough design review prior to release.

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Flexible and Rigid-Flex Circuit Design Principles, Part 5

04-27-2016

The outline profile of the flexible circuit is seldom uniform. One of the primary advantages of the flexible design is that the outline can be sculpted to fit into very oblique shapes. In this column, Vern Solberg focuses on outline planning, physical reinforcement, and accommodating bends and folds in flexible and rigid-flex circuits.

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Flexible and Rigid-Flex Circuit Design Principles, Part 4

03-30-2016

All of the design rules for the glass reinforced-portion of the board (land pattern geometry for mounting surface mount devices, solder mask and the like) are now well-established. One unique facet of fabricating the rigid-flex product is how the flexible portion of the circuit is incorporated with the rigid portion of the circuit. As a general rule for multilayer PCB design, furnish a balanced structure by building up the circuit layers in pairs (4, 6, 8 and so on).

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Flexible and Rigid-Flex Circuit Design Principles, Part 3

03-02-2016

This column focuses on methods for specifying base materials, and also address copper foil variations and fabrication documentation. It is important to research the various products in order to choose the one that best meets the design requirements.

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Flex and Rigid-Flex Circuit Design Principles, Part 2

02-19-2016

Flexible circuits are commonly developed to replace ordinary printed circuit board assemblies that rely on connectors and hardwire for interconnect.

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Flex and Rigid-Flex Circuit Design Principles, Part 1

01-27-2016

Flexible circuits represent an advanced approach to total electronics packaging, typically occupying a niche that replaces ordinary printed circuit board assemblies and the hard-wire interface needed to join assemblies.

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2005

PCB Designers Notebook: Flexible Circuit Design

01-03-2005

The flexible circuit was originally used as a conductive element for interfacing signals from one electronics assembly to another.

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