National Physical Laboratory

Condensation Project

Measuring Coating Protection Performance under Condensing Conditions: Invitation to Support Project

©iStock.com/dinadesign
©iStock.com/dinadesign
  • NPL has developed a new technique for achieving controlled condensing conditions on circuit boards.
  • NPL is proposing a Joint Industry Project (JIP), to characterise the effect of condensing conditions where conformal coatings are used to mitigate against the effect of liquid layers on electronics. NPL wishes to develop the technique with industry to produce a test method that meets industry needs.
  • NPL needs industry support to fund this development. A short webinar will be held to outline the scope of the project on Monday 30 November 2015. Find out more

Background

As electronics are applied into increasingly harsh conditions, conformal coatings are being increasingly used across a wide range of applications to mitigate against electrochemical failures. Humidity testing in combination with SIR (Surface Insulation Resistance) testing is used to characterise coatings, however a more severe test where a liquid layer is formed is finding popularity. The new test is required because it is more challenging to achieve coating coverage over right angle edges than for flat areas. These edges on the termination provide active sites on which electrochemical corrosion can proceed. The new tests aim to achieve condensing conditions where a liquid layer is formed. This is a more aggressive test for a coating, yet is representative of typical failure modes.

Humidity cabinets are engineered to achieve stable temperature and humidity conditions and to expressly avoid condensation occurring in them. Rapid transitions between conditions may cause condensation, but the occurrence and level is not predictable or repeatable. To improve the capability of creating condensation separate injection of moisture into the environment is currently being used, but again the effect is not predictable on circuit test board.

A New Development at NPL

A new approach of generating condensation on a test board has been developed. For this new approach, the condensation level on test samples can be accurately controlled, and the condensation period and cycles programmed independently of the humidity conditions set in the chamber. This accurate control is achieved by holding the test board at an independently controlled temperature. By depressing the temperature of the board below the ambient in the humidity chamber controlled levels of condensation can be achieved on the test board. Data taken from example tests are shown below during cyclic condensing events.

EI Condensation Project - Fig 1

These graphs show for three test board conditions in a climatic condition of 40 ºC / 93%RH, when the test board temperature is dropped to 38.5 ºC, what happens to the SIR. The first (top) graph shows the effect when the uncoated test board is dropped periodically from the ambient to 38.5ºC. The second (lower left) graph shows the effect for a 0.5 oz copper tracks covered with acrylic coating. The reduction in SIR has been reduced compared to the bare copper. However, the last (lower right) graph, which is for a 3 oz copper track (~100µm), shows the acrylic coating is not doing as good a job at covering the corner edges of the track, and during the condensing condition the SIR drops significantly. Note that this does not appear to be as significant with just the humidity condition, but with condensation we see a significant drop in SIR with this thick track.

Project Outline

This document sets out the project scope, with three areas being identified.

  • Develop and verify test parameters for condensation testing in an industry context.
    • Condensation level, condensation period and condensation cycles will be investigated to simulate the service conditions.
    • Condensation test parameters will be defined.
  • Validate the condensation test method using an assembly coated with different coatings and coated by different methods by the project partners.
    • As part of the project we will develop a suitable challenging test vehicle. The design will consider the range of components and the component layout to achieve coating challenges.

Project Flow

  • Agree experimental test board design
  • Partners agree on coating test assemblies and supply
  • Agreement on test conditions
  • NPL, or partner, builds test boards
  • Test assemblies circulated to partners for coating
  • NPL tests assemblies
  • NPL reports of Phase 1, and discuss outcomes with recommendations for Phase 2
  • Phase 2, consider optimisation of test vehicle, coating choice and application techniques, and test conditions
  • Repeat experimental procedure from Phase 1
  • NPL reports on Phase 2 and agrees with partners on test procedure.

Outputs and Partner Benefits

  • The project will produce a test method to evaluate coating protection performance when exposed to condensation.
  • Partners will have their coating and application method tested in this project, and will be able to benchmark to their peers.
  • Certain key points of information will be kept confidential to the project partners.
  • Any publication at conferences will be 12 months from first disclosure to the partners, and data will not specifically attributable to a partner.
  • Progress will be reported regularly, with meetings to be held where agreed.
  • Methodologies will be disseminated to standards organisations on project completion.

Contributions

The funding structure for this project is that government funds have been released to support this project, and a condensation system has been developed. The partners' contribution will help to develop the project further, and develop a condensation test method and use the method to evaluate coating protection performance in condensing conditions.

The project will take 12 months. The cost per partner is £6,500 per annum. Cash contributions from partners are essential for the work, while in-kind support are envisaged as a necessary part. In-kind contributions will include coating of the test assemblies, and possibly assistance with the assembly process.

To protect the investment of partners joining the project from the outset, restrictions may be applied to latecomers wishing to join the project

Actions

The project is holding a webinar on Monday 30 November 2015 - find out more

Contact

For further information, please contact Ling Zou

Last Updated: 14 Sep 2016
Created: 4 Nov 2015

Registration

Please note that the information will not be divulged to third parties, or used without your permission

Login