How to Avoid Press Fit Failures in High-Density PCB Designs

Press fit connectors are common in high-density PCB designs - powering 5G infrastructure, electric vehicles, aerospace systems, and advanced medical devices. Their ability to deliver high I/O counts without the heat risks of soldering makes them indispensable for modern electronics.

But here’s a hidden risk: If strain during insertion isn’t properly managed, it can lead to latent solder joint cracks, fractured plated through holes (PTHs), or deformed pins. These failures often escape detection during testing and only surface in the field - causing warranty returns, costly recalls, or even mission-critical system outages.

In this post, we’ll cover how stress impacts PCB reliability, safety thresholds, and how to overcome these challenges in your application.

Understanding Press Fit Strain

Press fit technology uses an interference fit, where connector pins are pressed into PTHs with near-zero clearance to form a tight mechanical and electrical bond. A controlled force (up to 600 lbs for a 60-pin connector) drives this process, causing the PCB to flex. This flexure generates strain that can crack solder joints, PTH barrels, or deform pins, threatening reliability in high-stakes applications like aerospace or medical devices.

For instance, a medical client could face costly MRI control board failures due to BGA cracks near press fit sites, underscoring the need for precise strain management.

Types of Press Fit Connectors

There are two main types of press-fit pins:

• Solid pins, which feature a rigid press-in zone
• Compliant pins, which have an elastic press-in zone that allows for flexibility and deformation during insertion

Both types of press-fits can be either soldered or solderless, depending on the application (pin count/density, risk of thermal stress during soldering, simplicity of assembly).

Press-fit pins are commonly used by many connector manufacturers and greatly improve system reliability and performance. The pin is a stamped metallic spring section sized slightly larger than the finished hole. During insertion, it elastically deforms and creates a continuous radial force against the PTH barrel, providing low contact resistance and mechanical stability.

The picture below shows a multispring press-fit pin from TE.

This press-fit pin can be applied to both low-density and high-density applications. The pictures below show very common connectors with press-fit pins that help provide mechanical support and low-resistance. Solder would typically be applied to this kind of connection.

For higher-density pin arrays (like the examples shown below), the connector can be inserted without the need for solder (picture taken from this whitepaper), but it may require a sophisticated tool for managing its insertion properly.

Though widely used, errors anywhere in the press-fit system (incorrect hole, uneven plating, contamination, incorrect insertion force) can produce latent defects that can survive visual inspection but fail under thermal cycling or vibration.

Why Strain Management Matters

As 5G, automotive, and aerospace applications demand higher signal speeds and pin counts, press-fit connectors are critical. Unmanaged strain can cause solder joint cracks, PTH barrel fractures, or pin deformation, leading to open circuits or latent failures. Strain decreases with distance, but factors like PCB thickness, asymmetric stack-ups (e.g., HDI, rigid-flex), or exotic laminates (e.g., metal core) amplify risks. For example, metal-core PCBs, common in high-heat applications, may require thicker fixtures to control flexure.

Common Failure Modes of Press-Fit Systems

• Improper plated-through-hole geometry (hourglass or non-uniform plating in high-aspect holes) reduces contact area and retention force, leading to early or intermittent failures.
• Over or undersized finished hole vs. pin compliance mismatch causes either excessive insertion force (PCB damage, cracking) or insufficient retention (low contact force, high resistance).
• Tin-soldering or “cosmetic” tinning of the compliant section compromises elasticity and can create brittle or intermittent interfaces; press-fit pins are typically engineered to work without tinning of the compliant zone.
• Contamination, poor cleanliness after fabrication, or mechanical misalignment during press insertion, leading to non-gas-tight joints and a higher failure likelihood during thermal cycling or vibration.

Recommended Design Process with Press-Fit Pin Connections

• Design and board fabrication
  1. Specify hole and plating targets from connector OEM drawings; include finished-hole diameter tolerances, plating thickness (specify heavier plating or controlled copper distribution for thick boards), and drill/plating process controls on fabricator drawings.
  2. Minimize aspect-ratio issues: avoid excessive board thickness where possible or use segmented designs to ensure uniform plating through the hole.
  3. Use high-Tg laminate and appropriate resin systems for high-temperature or vibration environments.
• Connector/pin selection
  1. Choose compliant-pin geometries rated for your application's current, insertion/retention force, and signal integrity needs (eye-of-needle, multispring/action-pin, crowned designs for power).
  2. For high-speed signal applications, select press-fit designs optimized for controlled launch and short compliant lengths to reduce signal discontinuity.
• Assembly and press process controls (primarily for higher pin-density applications that are solderless)
  1. Maintain a 1–2 mm clearance around press fit sites for dense assemblies to enhance safety
  2. Use controlled insertion tooling with force monitoring and stroke control (closed-loop presses) for high-density pins.
  3. Adopt fixtures and automated placement to ensure connector orientation and alignment before press; manual placement risks misalignment for dense/high-pin-count modules.
  4. Avoid soldering or tinning the compliant press-fit zone; do not “repair” loose pins by soldering—this masks root causes and creates unreliable joints.
• Inspection and verification (primarily for high-reliability applications)
  1. Use 2D X-ray to detect bent pins or PTH cracks; offline CT scanning reveals subtle defects
  2. Use post-insertion electrical resistance checks, pull/push retention testing on samples, and periodic cross-section metallography.
  3. Track insertion force histograms and resistance distributions as process control charts; use statistical process control to detect drift before field failures occur.

 X-ray inspection reveals hidden defects such as bent pins and cracked PTH barrels in press-fit assemblies.

Press-fit PCBA connectors are powerful enablers of high reliability, solderless and solderable interconnects when the entire press-fit system (connector design, PCB hole/plating quality, insertion tooling, inspection, and qualification) is treated as a single engineered solution.

Following OEM specs, using controlled insertion and inspection, avoiding counterproductive repairs, and incorporating an inspection and validation process are the practical steps that result in a high-reliability press-fit system.