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

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#82410

Questions About Risk of PCB Delamination as a Result of Moisture Build Up After Damage to Solder Mask | 23 April, 2019

Hi all and thanks for viewing my post!

My questions related to the subject line are as follows:

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

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

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

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

Thanks again for reading and I look forward to the advice from the community.

Best Regards, Josh

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#82417

Questions About Risk of PCB Delamination as a Result of Moisture Build Up After Damage to Solder Mask | 23 April, 2019

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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#82418

Questions About Risk of PCB Delamination as a Result of Moisture Build Up After Damage to Solder Mask | 23 April, 2019

Hi Dave,

Thanks a lot for your reply.

After doing some process work on a Laser Etching machine it was brought to my attention by a colleague that if the solder mask was being penetrated fully, we could be at risk for absorption of moisture leading to other problems.

Your answers fall in line with my assumptions about the inherent nature of moisture, FR4, and PCB delamination. I did, however, want an opinion since I am not a manufacturer.

Best Regards, Josh

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#82465

Questions About Risk of PCB Delamination as a Result of Moisture Build Up After Damage to Solder Mask | 29 April, 2019

Besides, regulated power supply should be installed separately on the printing boards. When power and circuits share the same printing boards, it should be avoided that regulated power supply and circuit components are mixed or power and circuits share the same ground wires, because this kind of routing will not only generate disturbance, also also makes it difficult to disconnect the load in maintenance. At that time, there is no other option but to cut part of the printing wires, which will damage the printing board.

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