Testing Flexible Circuits, Part I Chapter 2: Requirements and Procedures

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The IPC 6013 specification recognizes three classifications of flexible circuit boards based on end use applications and defines five types of circuits based on construction.

Performance is specified for the following types of circuit boards, which is taken directly from IPC 6013:

1.3.2 Printed Board Type Performance requirements are established for the different types of flexible printed boards, classified as follows:

Type 1 Single-sided flexible printed boards containing one conductive layer, with or without stiffeners.

Type 2 Double-sided flexible printed boards containing two conductive layers with plated-through holes (PTHs), with or without stiffeners.

Type 3 Multilayer flexible printed boards containing three or more conductive layers with PTHs, with or without stiffeners.

Type 4 Multilayer rigid and flexible material combinations containing three or more conductive layers with PTHs.

Type 5 Flexible or rigid-flex printed boards containing two or more conductive layers without PTHs

A flexible circuit that meets the requirements of IPC 6013 is considered a reliable product for most industries and applications; but what happens when a company has requirements that are not specified in this document? Actually this is fairly common as there many unique applications that, while not covered in this document, are ideal for flexible circuits.

First, many manufacturers have access to a comprehensive database of test results for a variety of applications; often these can be used as a reference point in determining the suitability for an application.

If there is no test data in a circuit manufacturer’s or material supplier’s archives, then it is fairly common that a specific test is developed. One common example is that a circuit needs to survive a submersion test in an unusual chemical. Simply dipping a circuit or circuit material in the chemical may be a very rough starting point, but it should never be considered a conclusive test. In order to truly determine if a given requirement can be met, it must be proven with statistical certainty. This often requires multiple tests and will require input and collaboration from material suppliers. The test itself needs to be statistically valid, so a qualified test engineer would need to design and perform the testing. Even if the test shows statistical confidence, subsequent sampling tests may need to be performed by the material fabricator, the flex manufacturer and/or the end user.

Sometimes, a material supplier is willing to certify that material can pass a certain test, in lieu of any ongoing testing. The end application is generally a significant factor in determining the level of pre-production testing. With applications ranging from toys and games to implantable and life sustaining functions, the level of testing required can vary greatly. Test regimens may take several months, and the supplier will “lock in” a process sequence and manufacturing procedure to best assure minimal variation among parts produced at different times.