Questions About Risk of PCB Delamination as a Result of Moisture Build Up After Damage to Solder Mask

Josh, are you setting someone up with these questions?

Answers to your questions related to the subject line follow:

Q1. Does the Epoxy Solder Mask Layer of a PCB protect against moisture absorption? Is this a primary function of the solder mask?

A1. The purpose of solder mask is to restrict solder from contacting traces and other conductive features on the board in selected locations and causing bridges between features.

You mentioned “epoxy solder mask layer.” Primary types of solder mask are: epoxy liquid, liquid photoimageable solder mask (LPSM or LPI) inks and dry-film photoimageable solder mask (DFSM).

Conformal coating is used to prevent moisture absorption. Common conformal coating materials are acrylic, epoxy, silicone, urethane, and parylene.

Q2. Does exposed FR4 naturally absorb moisture? If so, how harmful is the moisture?

A2. FR4 is naturally hydroscopic. If the moisture is managed or reduced to proper levels, it is not harmful. If not controlled, moisture absorbed by boards will expand at soldering temperatures. The resulting vapor pressure can cause: internal delamination and excessive strain on plated hole walls (e.g., post separation)

Q3. Has laser etching of an Epoxy Solder Mask Layer ever been known to be a root cause for moisture entering a PCB?

A3. Not that I’m aware of.

Q4. In a normal setting, is there risk for moisture to penetrate a PCB at its edges, panel breakaway locations, [sic and] surface mount and through hole locations, etc.?

A4. In a normal setting, if an assembler does not take precautions, the potential for moisture absorption in board exists.

For assemblers, IPC-1601 provides suggestions for proper: handling, packaging material and methods, environmental conditions and storage for boards. Look here for an overview of IPC-1602 – Printed Board Handling And Storage Guidelines [https://www.smta.org/chapters/files/Carolinas_Presentation1601.pdf]

IPC-6011 - Generic Performance. Specification for Printed Boards, 5.0 Preparation For Delivery, 5.1 Packaging. Printed boards shall be packed in accordance with minimum packaging which will afford adequate protection against corrosion, deterioration, and physical damage during shipment from the supply source to the first destination. Methods of packaging shall be determined by user requirements.

Find “Controlling Moisture in Printed Circuit Boards” Michael Pecht at CALCE [2011]. The paper focuses on moisture-related issues in PCBs and provides guidelines to reduce the impact of moisture on the reliability of printed circuitry boards. The controls and guidelines provided in the paper can be implemented at different stages of PCB production.

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