PCBA Press Fit Connector Reliability: PCB Strain Thresholds and Best Practices

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 either be 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 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 (picture taken from this whitepaper).

This press-fit pin can be applied both in 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.

B2B-PH-K-S by JST
source: digikey

PTT-102-01-L-S by Samtec
source: digikey

0457140001 by Molex
source: digikey

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 may require a sophisticated tool for managing its insertion properly.

Image source: TE

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 under-sized 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 higher failure likelihood during thermal cycling or vibration.

Get your PCBs Built & Assembled

San Francisco Circuits specializes in getting complex, high-end PCBs built fast, including flex, rigid-flex, metal core, and mil-spec.

We run by a simple motto with complex meaning: Bridging Concepts with Reality. Our specialty is the single-source supply of both bareboard and assembled PCBs, from standard builds to the most advanced technologies.

Many of our customers bring us designs that typical boardhouses can’t manufacture or assemble. We welcome that challenge. Whether it’s prototype or production, our expertise ensures high-quality multilayered PCBs delivered on time, even when requirements push beyond industry norms.

• Tailored Partnerships: Prototype or production, U.S. or overseas, we align your project with the best-fit facility for speed, cost, and compliance with industry standards (IPC, mil-spec, medical, computing).
• Advanced Testing: Strain gauge analysis, X-ray, CT scanning, and IPC-TM-650 testing ensure reliability in high-density designs.
• One-Stop Shop: You get end-to-end service under one roof, from bareboard fabrication to sourcing, assembly, and production.
• End-to-End Support: Our team provides expert consultation and rigorous quality control from prototype through production runs.