Applying IPC Ionic Contamination Specifications to Your Medical PCBA Development

February 28, 2020 , in Blog, Medical

In computational science, there is a well-known term concerning the results to be expected from a process based upon the input to it. That is, “garbage in, garbage out.” Although not linguistically elegant, this is technically accurate. The fact that the output from any system is determined in full or in part by the information or data provided to it for analysis, evaluation or modification is indisputable. Thus, care must be taken to ensure that inputs are accurate, pertinent, and pristine.

Cleaning a circuit board

Removing ionic contamination from a PCBA

Medical treatment today is highly dependent upon the functionality, quality, and reliability of electronic devices. These devices are driven by circuit boards that must adhere to PCB standards. In fact, every aspect of design, manufacturing, and testing of medical device PCBs is subject to or guided by standards and/or regulations. And the most important testing standard for ensuring your boards are well-built and pristine so that intended data and information signals, free of garbage, can be processed is IPC TM-650 Test Methods Manual.

One of the most significant forms of garbage on circuit boards is ionic contamination, which can cause major performance and reliability problems for medical devices, especially testing devices that rely on the precise interpretation of small signals for correct measurements. For example, ECG signals are typically 1mV or less. Therefore, it is very important, if not critical, that board cleaning and testing, such as defined in IPC TM-650 be applied during your medical PCBA development. Let’s explore the IPC ionic contamination specifications and how they can best be applied.

What Are the IPC Ionic Contamination Specifications?

As patient safety is the utmost concern of the medical device industry regulatory bodies, there are a number of test regimens utilized to ensure medical electronic devices do not pose any undue risk to patients or users. Many of these tests are established and classified by the International Electromechanical Commission (IEC) in standards IEC 60601 and IEC 61010. These tests are primarily end-product assessments that do necessitate your boards are manufactured for medical device testing; however, they do not directly provide for evaluating the PCBAs themselves or focus on ionic contamination.

The IPC TM-650 Test Methods Manual provides specifications for the following types of board testing.

IPC TM-650 Test Methods

  • Visual
  • Dimensional
  • Chemical
  • Mechanical
  • Electrical
  • Environmental
  • Connector

In addition to the test methods, which are too numerous to list here, for the types above, the manual also provides specifications for reporting results, testing conditions, measurement precision test equipment calibration. And included under Section 2.3 Chemical Test Methods for the ionic contamination specifications, shown below.

IPC Ionic Contamination Specifications

2.3.25D   Detection and Measurement of Ionizable Surface Contaminations by Resistivity of Solvent Extract (ROSE) 

Provides methods of utilizing ROSE testing to identify the level of ionic contamination on PCBs and PCBAs. Methods defined are i) manual extraction, ii) dynamic extraction, and iii) static extraction.

2.3.25.1   Ionic Cleanliness Testing of Bare PWBs

A process control test method whereby a ROSE tester and method is used to determine the surface extractable and board absorbed ionic content for a PCB.

2.3.28B   Ionic Analysis of Circuit Boards, Ion Chromatography Method

Defines a method of measuring the level of ionic contamination that can be extracted from the surface of PCBs and PCBAs using ion chromatography.

2.3.28.2   Bare Printed Board Cleanliness by Ion Chromatography

A method to ascertain the level of positive (anion) and negative (cation) residue on PCBs using ion chromatography.

Now, let’s see how to best apply these for medical PCBA development.

Applying the Best Ionic Contamination Mitigation Strategy

Building medical circuit boards requires a well-defined development plan to be efficient and effective. This plan should be comprised of and integrate multiple strategies, such as quality control and risk management. For medical PCBAs that require precision measurements, a strategy for mitigating iconic contamination should also be included. And for the best results, the strategy should utilize the IPC ionic contamination specifications, as is done below.

The Best Use of IPC Ionic Contamination Specifications

A. Determine whether to test and clean the PCB, PCBA or both.

B. For PCB, determine whether you need anion and cation concentration data. 

a. If yes, use 2.3.28.2 to determine ionic content.

i. If the content above tolerance, use 2.3.25.1 or 2.3.28B to determine the extractable amount of surface ionic content.

1. If the extractable amount is greater than 0 (or negligible)

a. Clean PCB

b. Go to B.a.

2. If the extractable amount is 0 (or negligible)

a. Go to C.

ii. If the content below tolerance, do not clean.

iii. Go to C.

b. If no, determine whether you need surface and absorption or surface only data.

i. If surface only, use 2.3.25D or 2.3.28.2 to determine surface ionic content.

1. Go to B.a.i.

ii. If surface and absorption, use 2.3.25.1 to determine the extractable amount of surface and absorption ionic content.

1. If the extractable amount is greater than 0 (or negligible)

a. Clean PCB

b. Go to B.b.ii.

2. If the extractable amount is 0 (or negligible)

a. Go to C.

C. For PCBA, use 2.35.25D to determine surface ionic content.

a. If the content above tolerance, use 2.3.28B to determine the extractable amount of surface ionic content.

i. If the extractable amount is greater than 0 (or negligible)

1. Clean PCB

2. Go to C.a.

ii. If the extractable amount is 0 (or negligible)

1. End process.

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Ionic contamination can be a serious problem for your medical PCBA development, if not adequately addressed. However, doing so requires that you partner with a contract manufacturer (CM) that has the equipment and expertise to perform the necessary testing. At Tempo Automation, we wash every board we produce and will perform IPC testing as required to ensure the ionic cleanliness of your medical devices PCBAs.

And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on IPC ionic contamination specifications or how to use them for your PCBA development, contact us.

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