Component Package Types: Selection Criteria

Key Takeaways

• Chip manufacturers must balance many (sometimes conflicting) design parameters for ICs.

• The primary differentiation between component package types is how they solder to the board.

• A list of some common package types designers will likely encounter.

Component package types run the gamut of shapes and sizes, sometimes even with identical functionality.

As electronics come in many shapes and sizes, so do the components that power their functionality. At first, designers may need help differentiating between the different component package types on product sheets, especially when the parameters do not differ. It’s easy to unknowingly purchase components that are too large, too small, or entirely incompatible with the design stage of the circuit. Every package has its benefits and drawbacks regarding size, cost, and effect on the board manufacturing process, and even older technologies can still provide the necessary performance for today’s electronics.

Motivation for Component Package Design

Form follows function, and that’s just as true for components as for any other engineered device. From a performance and manufacturability standpoint, ICs must balance four fundamental concerns:

• Encapsulation - The IC manufacturing process is meticulous and extremely sensitive to environmental contamination. Packaging must provide a physical barrier to prevent the ingress of moisture or solid matter that could short, corrode, or disrupt conduction paths.

• Handling - Packaging must be rugged enough to accommodate human and machine handling for assembly purposes.

• Heat dissipation - Heat is the enemy of electronic longevity and performance, eventually aging materials to the point of failure. Packaging must provide rigidity and safe handling without overly constricting heat flow out of the device.

• Insulation and isolation - Packaging also provides the substrate to support the necessary signal propagation speeds and characteristic impedance for components.

General packaging trends must balance size against pin count. Higher pin count and smaller package sizes promote high-density interconnect (HDI) design but are at odds with traditional manufacturing techniques. For the circuit designer, the cost will also be a factor: components that satisfy both conditions are more expensive up-front and may increase the manufacturing cost due to more exacting precision requirements.

Differentiating Methods of Assembly Integration

Packages can also sort according to their integration method with the board, which affects multiple board DFM aspects, including the layout density, production time, and applicable soldering process. These general component categories are:

• Through-hole (TH) - A package whose pins insert into and through the board; on average, these packages require considerably more space than SMT for the drilled holes. An older technology than the relatively recent SMT can prove more cost-efficient for some components, even considering the extra fabrication steps. For automated soldering, TH packages require a wave solder format that runs a wave of molten solder across the side of the board where the pins protrude. Newer components and product lines tend to skip TH technology entirely.

• Surface mount technology (SMT) - SMT uses planar leads on the mounting side of the components for soldering as opposed to the arching or vertical pins of TH packages. Since these component packages do not require drilling, the top and bottom layers of the board are fully utilizable (i.e., the integration of an SMT package on one side of the board does not affect the opposite side). Additionally, SMT packages usually have much smaller body dimensions than TH, further supporting HDI design. Costs may vary: simple passive and active devices may prove cheaper than TH packages due to economies of scale. However, more complex ICs may be pricier than analogous TH packages.

• Custom packages - Sometimes, the off-the-shelf component parameters do not meet design constraints. Product development can work with IC manufacturers to customize ICs and packages. As one might expect, this is an excessively cost-prohibitive option typically only suitable for mass production quantities.

A final point on component prices: designers may see IC packaging options in plastics or ceramics. Plastics offer adequate material properties for most applications and are far more cost-effective than ceramics, but demanding or high-reliability boards may require ceramics for superior performance.

A List of Common Component Package Types

Much like the prototypes they inhabit, component packages represent lineages of then-cutting-edge DFM techniques. IC design and board design have co-evolved to meet the needs of end users and manufacturing simultaneously:

• Dual in-line package (DIP) - A widely used through-hole package with a 2.54 mm/100 mil pitch and row spacing up to 15.24 mm/600 mil row spacing.
  • Skinny DIP - Contains the same pitch but a narrower body and lead spacing at 7.62 mm/300 mil.
  • Shrink DIP - A narrower pitch at 1.78 mm/70 mil.
  • Zigzag in-line package - A narrow body that presents a 1.27 mm/50 mil pitch between each pin at the bottom side of the package. However, the leads are alternatively bent to either side of the package body, resulting in two rows spaced at the standard 2.54 mm/100 mil pitch.
• Pin grid array - A package with many vertically aligned pins allows for significantly higher-density ICs. This format has largely fallen by the wayside in favor of ball grid array technology.
• Small out-line package (SOP) - An SMD package with a pitch of 1.27 mm/50 mil and gull-wing or J-shaped (in this case, SOJ) leads that can be mounted flat.
  • Shrink SOP - Any SOP with a pitch less than 1.27 mm/50 mil.
  • Thin SOP - A thinner package body with a mounting height of less than 1.27 mm/50 mil.
• Quad flat-lead package (QFP) - A fixed package dimension with a variable pitch where the L- or J-pins (in this case, QFJ) extend from all four sides of the package body. It can include heat dissipation options like sinks and spreaders.
  • Low-profile/thin QFP - Low-profile and thin QFPs have mold thicknesses less than 1.4 mm or between 1.0 and 1.27 mm, respectively.
• Ball grid array (BGA) - An extremely dense package highly representative of modern HDI designs. Depending on the pitch, it may require additional fabrication methods for signal breakout.

Cadence Software Is the All-in-One ECAD Package

Component package types come in many sizes and styles. While it may initially seem daunting, circuit designers will quickly realize the advantages and disadvantages of the various packages after working with a few layouts. Given the current global IC shortage, the ability to pivot designs around the availability of packages is a handy skill in the short and long term. Cadence’s PCB Design and Analysis Software suite supports a fluid workflow with a vast component catalog in PSpice to update and simulate designs quickly. Once the design is ready for layout, OrCAD PCB Designer supports a seamless process from schematic to DFM board files.

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