Why a Dye and Pry Test Is Used in Circuit Repair

December 4, 2019

Dye and pry testing, which is sometimes referred to as a dye penetrant test, is done to identify concealed discontinuities that are found below various SMT components. It should also be noted that dye and pry testing is destructive. Still, the harmful component is for the greater good, as it is currently the most cost-effective and efficient method to analyze 100% solder connections of SMT packages that are bottom terminated, as well as BGAs.

Furthermore, any leaks or cracks that have developed on SMT parts that have been sealed can also be confirmed via dye and pry testing. Here, we will discuss dye and pry testing, how it works, as well as compare and contrast it to the microsection process.

How Dye and Pry Testing Works

In order to begin the sample preparation, the part of the board that contains the target feature is extracted. In some instances, the engineer may use a state of the art saw blade that is specially designed to cut circuit boards in a highly precise manner.

Proper technique, as well as the ideal tools, should be used during the initial step, as shear forces or vibrations can deleteriously affect the integrity of the sample in question and may also lead to novel defects.

After the excision component has been completed, the sample will be inserted into a vacuum chamber and will be engulfed in a dye that has low viscosity properties. Capillary actions are then triggered to pull the liquid dye to and fro so that it reaches every void and crevice without compromise. Interestingly, the pressure differential that is triggered by the chamber will help in this process.

Next, after the dye has been fully immersed, the sample will then be dried by inserting it into a top of the line moisture removal oven. Once the sample has been baked it will be fixtured prudently into a puller assembly unit so that the component can be separated from the board.

Finally, the qualitative assurance phase will take place, whereby both the component and its associated board will be assessed under a high magnification microscope, and any anomalies or defects that are found can be recorded and imaged for posterity.

Microsection vs. Dye and Pry Testing

Both microsection and dye and pry testing have their merits when it comes to the failure analysis of components that are bottom terminated, as well as for process validation. However, they have unique advantages and disadvantages that you should be aware of, as one process may be superior to the other, depending on what you’re working on.

For instance, if failure analysis is a priority, then it is recommended that you begin with either visual microscopy, a CT X-ray, or a conventional radiograph. By doing so, the sample will remain intact. As for destructive analysis, if it seems to be indicated, then several questions must be asked to facilitate the investigative strategy.

Consider the following: Is it paramount that the root cause is identified, or would it suffice to rule out or confirm a solder-based defect? You should also look into the prior troubleshooting reveal in regards to the failure mode, and should also determine if you have already identified the location of the problem pins and circuits.

Also, you will need to determine the budgetary limitations of your project as well as how many samples you can realistically afford to eradicate.

As for process validation, the questions you may need to ask yourself will likely be easier to answer. The needs of the end-user will likely drive most of the questions. For example, you will need to determine how many boards need to be analyzed as well as how many of each type of connection (SMT), for each board, needs to be assessed?

In sum, dye and pry testing yields a lower cost per joint, and the preparation time for samples is relatively modest. Moreover, you will be able to look at 100% solder connections at the same time. Limited data, however, is an issue with dye and pry testing, as you can identify the horizontal point of separation as well as yes or no opens if needed, but not much else.

As for microsection, it has a higher cost, as well as longer prep time for samples, given the fact that multi-step polishing and potting are involved with micro-sectioning. You will also need to select the absolute best target plane, as you will only be able to look at one solder connection row per cross-section.

However, one of the advantages that microsection has over dye and pry testing is that it will yield detailed data. This may include solder wetting angles, intermetallic layers, grain structure, fracture propagation paths, and voiding.

Dye and pry testing allow engineers to detect open circuits as well as cracking in BGA solder joints, which is why it is considered an excellent failure analysis technique in the industry. It can also be used to assess an entire ball grid array, which may comprise several hundred solder joints.

As a result, it is superior in many ways to other destructive processes in the industry, such as cross-sectioning. Dye and pry may also be used to identify a myriad of failure modes. For instance, it may be implemented to detect thermal cycling, thermal shock, mechanical shock or drop, solder joint fractures and pad cratering.

If you would like to learn more about the benefits of dye and pry testing, call Circuits Central at 1-888-821-7746 or contact us here.

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