ICT PCB Design Specifications – A Complete Guide

An ICT PCB has specific design requirements. For instance, the designer must know where to place test points, their proper spacing, and size. This guide explains all you need to know about the board. Learn how designers optimize it for the test and much more.

What is ICT PCB?

An ICT PCB is a circuit board designed for the ICT test. ICT is in-circuit testing in full. It describes a process manufacturers use to detect PCB and PCBA flaws. The test involves placing the board on a specially designed fixture.

The fixture contains a network of needle-like probes called test pins. These contact the board at various points, completing circuits. These circuits check the correctness of individual board parts and components.

The ICT system also includes a custom program. This program directs the testing process using the board’s design data. It allows the testing expert to automate most steps, enhancing precision and making results more reliable.

ICT PCB Features and Specifications

The board has test points placed at specified locations. The points can be of various types, including pads, hooks, and component leads. You can also use vias to reach the inner layers and check their circuits.

Test points must bear clear markings for identification. Their location can also hinder or allow probing. Standard practice places them on the PCB’s bottom side: it has more space for easier access.

In double-sided boards, the designer chooses the side with the least components. As we will learn later, component height also impacts the location of ICT contacts.

What Does ICT PCB Testing Check?

The in-circuit process checks design, fabrication, and assembly flaws. As such, we use it to test circuit boards before and after mounting them with parts. It assesses them for various problems, as explained below.

Bare PCB ICT Test

Bare boards contain conductive paths called traces and plated holes called vias. The in-circuit test checks them to detect the following errors before assembly:

• Opens caused by broken traces
  
• Shorted traces
  
• Via formation and conduction problems
  
• Trace impedance issues
  
• Inductance and capacitance value variations
  

ICT in PCB Assembly

The procedure also verifies circuit boards after populating them with electronic devices. Here, the steps are more advanced. The following is a list of the flaws it can detect.

• Short circuits and open circuits
  
• Missing components and improper placement
  
• Component orientation problems
  
• Incorrect component values
  
• Damaged components
  
• Soldering defects like bridges
  

In-Circuit Testing Methods

PCB manufacturers conduct in-circuit tests in two ways. One of them is the standard method called a bed of nails. It derives this name from the array of pins that characterize its fixture.

There’s also the flying probe method. This tester has pins hovering above the PCB. The pins occasionally descend to contact the board, completing circuits to check components. Each ICT system has its advantages and disadvantages.

The standard process is faster and more cost-effective. These attributes make it best for higher board volumes. In comparison, the flying probe test is a much slower method. This drawback makes it less suitable for large production runs. Automation also causes it to cost more.

Benefits of PCB ICT Test

In-circuit testing, ICT, is a crucial quality control procedure when making PCBs and PCB assemblies. It has these benefits: improved coverage and speed, high precision and accuracy, and consistency.

Test Coverage and Speed

The testing equipment covers more space, checking multiple nets at once. This feature makes it fast, which is advantageous in mass production or high board volumes.

High Precision and Accuracy

The pins connect to conductive points to check individual components, which increases precision. That, in turn, helps the manufacturer to quickly and accurately detect flaws.

Consistency Benefits

The test fixture and software are specific to the circuit board type. This feature means enhanced consistency in the testing steps. It also allows the manufacturers to repeat the test for similar boards without requiring adjustments.

How Do You Design an ICT PCB?

The person creating a circuit board for the ICT process must follow various design rules. These include placing test points where probes can establish contact without hindrance, among other requirements.

Various design programs come with schematic tools to help you determine test locations. These allow you to optimize the design for the process based on whether the test involves traditional or newer probes.

Traditional probes can effectively contact test points between 0.20 and 0.024 inches in size. On the other hand, newer probes can use contacts as small as 0.012 inches.

ICT PCB Design Guidelines

The success of any ICT process depends on how well the designer understands its requirements. In other words, they must refrain from practices that could make the process difficult or less efficient. The following are the dos and don’ts when creating an ICT test PCB.

Test Point Placement and Size

• Place test points on the side with fewer parts, which is usually the bottom of single-sided boards
  
• Space them evenly across the board to avoid damage and other problems
  
• Industry standards recommend a 3.20 mm margin from the board edges
  
• Ensure at least an ICT contact for every net
  
• Use more than two points if the net has a low-impedance part
  
• Space probe sites with a minimum of 2.50 mm distance from the center of one point to the other
  
• Only use small diameter vias (0.36 mm) or less as test points
  

Component Type and Height

• Avoid placing test points and tall components on the same side. They will hinder probing
  
• Only use through-hole parts leads as ICT contacts if they are sturdy enough to withstand the pressure
  
• Maintain 2.0 mm clearance for devices taller than 2.60 mm and 5.0 mm for those taller than 6.40 mm
  

Tooling Holes

• Have a minimum of two tooling holes on the board to hold it in place
  
• Place the holes on the board’s opposite sides
  
• Correctly size the holes, ensuring their diameter remains less than 3.20 mm
  

ICT PCB Testing Standards

In-circuit testing follows industry standards to ensure product quality and reliability. Various organizations write these standards, with requirements varying based on circuit board types and applications. They include the following:

• Institute for Printed Circuits, IPC
  
• Institute of Electrical and Electronic Engineers, IEEE
  
• International Electro-technical Commission, IEC
  
• Joint Electron Device Engineering Council, JEDEC
  

Regional bodies like the German DIN and Japanese JIS also provide electronics manufacturing guidelines. However, these standards are location-specific. They do not apply universally. The manufacturer chooses the standard to use based on the particular market.

Conclusion

A few rules apply when creating an ICT PCB. They include proper test point placement, edge clearance, and component-to-test point spacing. Optimizing the design ensures the ICT probes can contact designated ICT pads and other points unhindered. The designer must also follow the required testing standards as this guide outlines.