Understanding How Residues Cause Problems and Where They Come From

By Foresite

If you’ve ever chased an intermittent failure that disappears on the bench, or dealt with a “no trouble found” return that comes back again, this presentation is for you.

Foresite President Terry Munson walks through a practical, failure-focused view of residues: how they create electrical risk, why the same assembly can pass today and fail tomorrow, and where contamination actually comes from across the full manufacturing chain. 

The core idea: residues aren’t just “flux leftovers.” Contamination can originate from multiple places: board fabrication, component processing, assembly operations, cleaning chemistry, coatings, packaging, and even the end-use environment. Those variables can stack in ways that create either benign outcomes or very expensive problems.

What you’ll learn in the video

1) The three conditions behind dendrite shorts (ECM)

• A voltage differential (power vs. ground)

• Moisture that creates a conductive bridge

• A corrosive residue that acts as an electrolyte

When those align, metal can dissolve, migrate, and deposit—forming conductive paths that can short, “blow open,” and regrow depending on moisture availability.

2) Why low-standoff parts are a residue trap
Bottom-terminated components (like QFNs) and other low-clearance geometries can hold residues in a soft, moisture-attractive state under the part—even when the visible perimeter looks hard and “clean.” That’s where parasitic leakage and intermittent behavior often starts.

3) Where residues really come from (beyond assembly)
The talk maps contamination sources across:

• Fabrication wet chemistry and rinse-water quality

• Component plating/sawing processes

• No-clean + selective soldering scenarios where residues reach areas that don’t see enough heat activation

• Cleaning processes that solubilize residues but don’t effectively rinse under tight gaps

• Environmental outgassing (including sulfur-bearing materials) that can trigger corrosion mechanisms

Why this matters

Reliability failures tied to residues aren’t always dramatic at first. Many start as soft shorts, leakage, or intermittent performance—exactly the kind of issue that burns engineering time and warranty budgets. This session gives a framework for connecting residue chemistry to electrical behavior, so teams can move from guesswork to root cause.

Watch the full presentation and share it with anyone working in fabrication, SMT, selective solder, cleaning, conformal coating, or failure analysis.