Senior Technical Advisor at Elmatica

News from the Chair – cleanliness, thickness, inspection, and wicking!

Cleanliness, solder mask thickness, inspection, and wicking! How will the demands for these factors be presented in the revised edition of IPC 6012-DA?

The Automotive Addendum task group has existed since November 2014. The first edition of IPC 6012-DA was released in April 2016. We are now working on the revised version, expected a release in Q2 2018. As standards need to evolve, develop and follow the needs of the industry, this work is continuous. This blog post will address some of the challenges the group faces and some of the issues we want to avoid by revising IPC 6012-DA. The Automotive industry is an industry with high volume production, this need to be considered when developing a standard further.

First challenge – cleanliness
We have so far focused on four areas for improvement. One of these are the requirements and test methods for cleanliness in printed circuits.

The test requirements for cleanliness or Ionic Contamination used today are from the 80ties and don’t fill the demands for today’s printed circuits, as these consist of more advanced technology and requirements than in the 80ties.

However, new ways and equipment to test cleanliness have recently been developed. As soon as the methods have been thoroughly tested, they can be implemented as a demand in IPC 6012-DA. Tight communication with the IPC task group for cleanliness and continuous monitoring of the development and progress is the way to move forward. However, the group, have decided that the methods are so promising, that we will implement them in the revised addendum, as a recommendation, not a demand.

With Industry 4.0 there were changes
When the Automotive Industry embraced Industry 4.0 the demands for more complex and small-scale electronics increased. Smaller and more complex printed circuits naturally increase the need for testing of cleanliness as well. The challenge is when the test methods are not equally developed and as advanced as the printed circuits. It’s like building a new kitchen but keeping the old and malfunctioning appliances.

The methods were designed for process-control, not lot qualifications, as many believe and expect them to do. In reality, we still don’t have a sufficient and fast test method to do a proper lot qualification.

Another issue that recently has been brought up in discussions with test laboratories and internally in the Automotive Addendum task group is the ability to test local areas. Today’s methods measure the cleanliness of the entire printed circuit and are not able to find and locate local contaminated areas. To control quality and reliability you need the ability to measure cleanliness in those critical areas.  New tools will make this possible, and it is a priority for the task group to evaluate and qualify improved methods to check the cleanliness of a specific area.

In addition to new test methods, we are also discussing at what time in the production process we should do the testing. Performing a cleanliness-test of your printed circuit, before soldering may provide a result contaminated by natural substances from solder mask. We believe this will vary by solder mask curing and hard to control. A solution on how to avoid this could be to send the bare PCB through a reflow process and perform a test on this one since reflow will give the PCB an additional cure. This theory has been supported by a test report provided by Bosch.

A standard for solder mask thickness
The second challenge we spend much time on these days is the thickness of solder mask. The industry currently operates with two standards, standard a and b, referring to application methods.
The group has reached the conclusion that this is not optimal. We consider adding a demand for a specific thickness, suitable for all application methods. A demand that will meet the requirements and still be manufacturable.

Expect better inspection
Our third focus is level of inspections and inspection methods on the finished board. IPC requires that the inspections are after certain AQL (acceptable quality limit) demands.

Automotive production requires 100% visual inspection. With the volume in this industry, and with increased miniaturization, a 100% visual inspection by an operator is not practical. Implementation of Automated Visual Inspection is under discussion in the task group and will be added to the standard as a recommendation.

How do we actually measure wicking?
Another issue that has been addressed by the task group lately, is wicking, and how this is measured. According to our experience, the parameters provided by IPC is at its best confusing.

IPC requires that wicking is measured from the drilled hole edge to the point where the wicking ends. This might result in a false result where you don’t measure the wicking itself. In the new and revised edition of the Automotive Addendum, we will precise that the measurement should start and stop where the wicking start and stops. Only then will the results be correct.

Standards for PCB production specifications need to be alive and kicking, facilitating a modern production that meets the demands of today, not the ones in the past. As chair and member in several task groups, I know how much work lays behind a standard. The whole idea with task groups is to work dedicated towards an improvement, securing that all needs and consequences are considered and monitor the challenges from all stages of production. We need to extract knowledge from production files and convert it into useful information to improve the standards so they match the demands not only from IPC but also the industry.

With that in mind, I believe we also need a digital article specification that picks up requirements from all bits in the supply chain, but that is another topic. :).

Senior Technical Advisor at Elmatica, Jan Pedersen

 

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