What is MIL STD 275

To learn what is MIL STD 275, consider the following parameters and CAD tool options to work on getting your device into manufacturing and fabrication.

ALTIUM DESIGNER

Find the right software that can get your circuit board up to compliance standards.

Originally issued during the mid-1970s, MIL-STD-275 covered requirements for printed circuit board wiring. The standard underscored the quality of the conductors, the width between traces, trace thickness, and routing. After several updates of the standard through the 1980s and 1990s, the Department of Defense cancelled the standard during 1994.

Although MIL-STD-275E no longer exists as a regulatory, the Department of Defense refers to two IPC (Association Connecting Electronics Industries) standards that define PCB design and fabrication requirements for boards produced for military use. PCB designers and fabricators must comply with the IPC-2221 “Generic Standard on Printed Board Design“ or the IPC–D–275, “Design Standard for Rigid Printed Boards and Rigid Board Assemblies.” The IPC standards cover the electrical, mechanical, and thermal performance of printed circuit boards and the interactions that occur when change in design alters performance. As an example, the standard may consider the impact of increasing dielectric thickness to ground on lateral crosstalk and—ultimately—the performance of the PCB.

Because the standards focus on electrical, mechanical, and thermal interactions, complying with the standard requires PCB design teams and fabricators to consider a wide range of issues. For example, the standards address the initial schematic diagram, component designations, designation of electrical functions, shielding, grounding, and power distribution requirements. Other issues covered by the IPC standards include environmental conditions, component/circuit density, coatings, component placement, mounting holes, the placement of brackets and hardware, conductor routing, conductor width, board shape and size, and connector contacts. In addition, the standards cover ESD sensitivity, board flexibility, substrate materials, signal integrity, the number of signal layers, design reuse and other factors.

Design Teams Use Altium Designer to Meet the IPC Standards

Because Altium Designer functions within a unified design environment, design teams can rely on the software to match the scope and depth of PCB design requirements specified by the successors to the MIL-275 standard. The unified environment found within Altium Designer combines design rule checks, electrical rule checks, and simulations to ensure design and product quality.

Correctly defining constraints through Altium Designer’s Design Rule Checker (DRC) establishes specific design guidelines for the PCB components, schematic, and layout and provides the optimal electrical and mechanical specifications. Design teams use Altium’s Design Rules Checker along with these tools when considering basic material properties, dielectric requirements, circuit fabrication reliability, and end-use performance.

Another example of the unified design approach involves the use of the PCB Editor and Layer Stack Manager in Altium Designer to select the appropriate dielectric materials, specify the dielectric constant, and establish the layer thickness. For multi-layer PCB designs used for military applications, Altium Designer simplifies every part of the process and allows designers to set the number and thickness of layers for achieving the correct capacitance.

Risk-Management Design Platforms Enable Secure Designing

By providing an end-to-end design platform that includes integrated tools, the unified environment of Altium Designer moves the PCB design from schematic to documentation and to fabrication. With the use of the integrated tools found within Altium Designer, any member of an electrical design team can easily solve design issues with dielectric materials, the number of dielectric layers, and dielectric thickness.

Along with using PCB Editor to establish a good layout, designers can use the Schematic Editor select and place components to control electromagnetic interference (EMI) and eliminate the possibility of electrostatic discharge (ESD). As an example, Altium Designer provides the capability to interactively rout traces and components to curb increases in electromagnetic interference. The correct placement of components and good routing practices reduce the opportunities for radiated EMI along with the noise spikes, ringing, and resistive losses that cause voltage errors.

• Learn more about minimizing EMI in communications devices.
• Learn more about high-speed design and how it relates with a strong design platform.
• Learn more about HDI materials.

Achieve the Correct Component/Circuit Clearances with Altium Designer

Altium Designer protects against design flaws that reduce clearances through design rules that address every aspect of a PCB design. As a circuit design transitions from concept to schematic and to PCB layout, the design rules establish instructions for the PCB Editor. Because the design rules define routing widths, clearances, routing through styles, and plane connections, the correct application of the design rules also establish the appropriate component-to-component and component to board clearances.

Width and Clearance Rules Define Routing

Defining the width and clearance for the routing establishes the correct routing for fabricator requirements and IPC standard compliance. With the routing width and clearance established, design teams can use Altium’s PCB Editor to define the PCB area available for component placement and routing. The PCB Editor maximizes the free space between components by placing similar-sized surface mount components opposite one another on double-sided boards and by placing components on pads established to a regular grid.

Design teams may also use the Electrical Clearance Constraint function to define the clearance between electrical objects belonging to different nets. Altium’s Board Shape function matches the shape defined by a set of objects on one of the mechanical layers of the PCB. Design teams also have the option of assigning a layer sub-stack to a specific region of the board shape.

• Learn more about custom rules integration.
• Learn more about using rules-driven design to control a high-frequency board.
• Learn more about trace spacing and other requirements for getting a board through manufacturing.

Take a software that has its own IPC compliance wizard

Use Altium’s Interactive Routing Tools to Comply with PCB Design Standards

Altium’s interactive routing provides the precision needed for an IPC-compliant PCB layout. Interactive routing uses algorithms that follow electrical and routing rule definitions to determine the correct route path. Using the Routing Width Design rule and Track Width Mode setting within interactive routing eliminates the possibility of routing conflicts, collisions, and errors. Both tools establish constraints for the trace widths. The Routing Conflict Resolution mode prompts the router to respond to existing objects and apply a conflict resolution strategy.

Because the Interactive Routing function follows design rules and electric rules, the routing tool also supports Design for Manufacturability compliance requirements. Design teams can set the trace width and distances while selecting the corner style that eliminates sharp corners. Altium’s Interactive Routing function allows design teams to precisely place components. With the dynamically optimized connection tool found in the PCB Editor, design teams can establish shorter, untangled connection lines.

Active BOM Supports IPC Standards Compliance

Within Altium Designer, the Active BOM tool functions as a Bill of Materials editor and offers real-time information component specifications, availability, costs, and suppliers for design teams. Active BOM shows components placed in the schematic, displays fasteners, the blank PCB, and mounting glues as well as automatic and manual numbering.

Given these capabilities, teams can avoid the redesign of a PCB that can occur because of supply chain problems. Using the Active BOM toolset decreases design cycle delays and responds to Design for Manufacturability (DFM) and design reuse requirements found in the IPC standards by applying best practices for selecting parts that simplify fabrication and establish circuit designs and layouts available for use with other designs.

• Learn more about working with IPC compliant footprint models.
• Learn more about reusable batch output configurations.
• Learn more about the seamless PCB drawing process offered by Altium Designer

Manage the production of your manufacturing output files

The IPC-2221 and IPC–D–275 standards provide a broad framework for designing and producing printed circuit boards that can withstand harsh environmental conditions while delivering high quality performance. Altium’s unified design environment places all the necessary tools and functions needed to comply with those requirements within one software application. Design teams and fabricators can safely and precisely meet requirements for producing military standard PCBs without jumping from one application to another.