What to Look for in SMD Component Datasheets

 

If you want to learn more, please visit our website Standard Smd Package Sizes.

SMD components are not going away anytime soon, thanks to their low cost and low profile. SMD components come in a variety of standardized packages that make manufacturing and assembly with automated equipment much easier. The size of an SMD component can range from a large FPGA measuring inches across to a small resistor measuring just a couple mm. These components have standardized rectangular packaging, but they require small land patterns for soldering electrical connections on a PCB.

Where can you get the most accurate information on the land patterns you need to create for your components? If you download a component model from a forum or parts aggregator, the footprint may match the dimensions shown in SMD component datasheets, but the land patterns may need to be modified to prevent some common PCB assembly defects due to mis-sized lands. If you can access SMD component datasheets and verified footprints before you create your land pattern, you can prevent some extra engineering expense and ensure you comply with DFM guidelines.

Building Footprints vs. Land Patterns

The terms &#;land pattern&#; and &#;PCB footprint&#; for SMD components are sometimes used interchangeably, but they are not exactly the same. If you&#;re creating a model for 2D or 3D CAD models for a component, you need to differentiate between the body of the component itself and its land patterns. Note &#;land pattern&#; also applies to through-hole components, but it refers to the arrangement of holes for mounting the component on the board.

Here&#;s the difference between the two: the land pattern refers to the arrangement of pads (and possibly vias for fine-pitch BGAs) that are placed on the PCB. The footprint sometimes simply refers to the physical outline of the component, although it could also collectively refer to the combined land pattern + silkscreen outline/RefDes + courtyard + solder mask opening, all rolled into a single model. In some PCB design software packages, this is the meaning given to &#;PCB footprint;&#; you&#;re placing the land pattern, silkscreen information, mechanical outline, and courtyard definition in multiple electrical and mechanical layers in your design.

 

The image above shows all the different pieces of information that go into an SMD component. Obviously, an SMD component is more than its silkscreen outline and land pattern. What you also see is the landing pad size and solder mask opening, not the size of the leads. If you know what to look for in SMD component datasheets, you can easily build the right land patterns for your components.

What to Look for in SMD Component Datasheets

If you&#;re in the mood to create SMD component symbols and footprints from datasheets, you&#;ll need to remember the land pattern does not perfectly match the pad arrangement or body outline. The body dimensions of the component should be clearly listed in a mechanical drawing and can be easily replicated in your CAD tools. This will help you define the ideal silkscreen outline in your PCB footprint.

When drawing a landing pattern from SMD component datasheets, it&#;s important to remember the landing pattern in a datasheet is only a recommendation. Some datasheets will just show the pad sizes and will allow you to determine the best landing pattern. You&#;ll need to determine the best pad size in your land pattern and solder mask opening. Be sure your final footprint complies with the requirements for the standard you are working with: IPC-B as an industry standard, or perhaps internal/customer standards for a more custom package. 

CAD drawing showing pad arrangement on the LM393BIDR from Texas Instruments.

 

The CAD drawing shown above is common in SMD component datasheets. The pad arrangement is not a land pattern, it&#;s simply a mechanical drawing that you can use to design a pad arrangement for your PCB footprint. The pads used for soldering and mounting on a PCB will extend outward around the lead outline. The distance between neighboring pads and the solder mask opening around each pads should be large enough to prevent bridging during soldering.

All information on lead sizes, package dimensions, and recommended landing pads can be found in SMD component datasheets. If you want to get accurate component models alongside datasheets and sourcing information, there are some online options for finding the data you need.

Get Your Datasheets and Component Models in One Place

If you&#;re looking for SMD component datasheets with accurate information and full electrical specifications, there are a number of resources available. Distributors will generally provide datasheets for most of the components they sell and larger manufacturers will make these datasheets available on their websites. If you need to compare component specs and prices, get aggregated sourcing data, and find component models, you need to use the right components search engine. These services aggregate these data in one place, giving you a one-stop shop for multiple parts.

When you use the parts search features in Ultra Librarian, you&#;ll have immediate access to verified PCB footprints, schematic symbols, and 3D models for your components. You&#;ll also have access to SMD component datasheets, and all at no cost to you. You&#;ll have everything you need to customize component models for your new board and import them into popular ECAD applications. You&#;ll also have access to sourcing information from worldwide distributors.

Manually creating design libraries for SMD components takes most teams dedicated resources and time, but Ultra Librarian helps by streamlining this process. Working with Ultra Librarian sets up your team for success to ensure any design is going through production and validation with accurate models and footprints to work from. Register today for free!

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.

Design for Manufacturing (DFM) Demands for Component Packaging

Multi-pin I/O

Increasing pin I/O allows for greater functionality on a single die.

Miniaturization

For more information, please visit Standard Smd Sizes.

Smaller packages mean reduced weight, form factor, and higher circuit density.

Heat Resistance

A reduction in heat sensitivity means greater integration with automated soldering techniques./p>

Heat Dissipation

A component that is faster at ridding itself of heat can operate at higher speeds and powers.

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.

Grouping Common Package Characteristics

Larger Size

Smaller Size

Lower Pin Count

DIP, skinny DIP, ZIP, SOP, SOJ, QFJ

SSOP, TSOP, TQFP

Higher Pin Count

Shrink DIP, PGA

QFP, TCP, BGA, CSP

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.

Leading electronics providers rely on Cadence products to optimize power, space, and energy needs for a wide variety of market applications. To learn more about our innovative solutions, talk to our team of experts or subscribe to our YouTube channel.

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