Editor’s note: This blog post was originally written in 2016 and has since been revised and republished for maximum accuracy.
Potting is the process of filling or submersing a complete electronic assembly using a compound material. Original equipment manufacturers (OEMs) may want their assemblies potted for a number of reasons, but typically it is carried out to protect against shock and vibration, or to stop moisture or corrosive agents from getting near the electronics.
While the process may sound quite simple - just a case of pouring liquid resin into an enclosure - it can actually be a real challenge for those carrying it out. To achieve the "perfect pot", there are a number of factors to take into consideration, to ensure that the dispensed potting material is consistent and repeatable.
In this blog post, we will look at six steps that must be followed, in order achieve a consistent result. Also included are some of hints and tips for those involved in carrying out the process within electronics manufacturing.
1. Resin temperature
It is important to heat the resin up before the potting process starts. This allows the potting mixture to flow better through the system when production begins. Due to the wide range of resins available, it’s important to consult the supplier of the resin so they can advise what the optimum flow temperature should be.
2. Resin and hardener ratio
For some resin and hardener systems, the weight ratio can be varied to produce cured material with differences in properties, usually in flexibility or hardness. Again, we recommend you consult with the supplier to determine if the mixing ratio is fixed or if some variation is possible. To achieve the optimum result for your own application, you may need to run a number of trials before production volumes commence.
Broadly speaking, there are two types of potting methods available. A cylinder-piston machine contains cylinders for the resin and hardener that are sized, so the volume ratio is that of the potting compound. When the pistons are inserted into the cylinders, the correct proportion is pushed into the mixing area.
The alternative method to this uses a gear pump and allows more control over the ratios. This method uses screws that are turned by separate motors controlled by electronics. As the screws turn at the correct speed, they dispense the resin and hardener in the correct ratio. While this method does offer more control, the machines themselves are usually more expensive to buy.
3. Mix of material
Once the ratios have been controlled the resin and hardener require mixing together. This operation is typically achieved using a detachable mixing nozzle. It’s important the nozzles are detachable as once the mixing process has taken place they have a short life span due to the curing process and, therefore, need regularly replacing.
Mixing nozzles ensure optimum performance by dividing and recombining the materials into a homogeneous stream, and it’s generally accepted that the longer the nozzle, the better mix of material.
4. Force of mix
It is important for the materials to be mixed at pressure so that they are combined effectively. If there is too little pressure, then this can result in an uneven mix. If you are unsure of the exact pressure you need or have experienced issues with your current settings, contact the supplier of the materials for advice.
5. Dispense volume/weight
The required volume or weight of the mixed material can be achieved in multiple shots or one single controlled shot. Much depends on the size of the electronic assembly that is being potted. A cylinder-piston method can be adjusted to regulate the dispense amount but is limited by the cylinder size. As a result, in most cases multiple shots are required. In contrast, a machine with a gear pump allows a single continuous shot, which can be set and controlled electronically.
6. Dispense speed
This will be closely related to the force of mix and the required volume/weight. Of course, from the operator's perspective, the speed that the mixture is dispensed must be at a rate they are able to cope with on the assembly line in a controlled manner.
In addition to the above steps, here are some further hints and tips, many of which are the result of our very own blood sweat and tears!
- Always ensure that you have suitable ventilation and extraction systems in place as some hardener materials are hazardous.
- Always ensure that appropriate health and safety measures are taken as recommended by the material suppliers. Gloves and safety glasses should be worn as a minimum.
- Always protect the resin and hardener from moisture to avoid contamination and poor potting results.
- Make sure you mix the resin material before production if it hasn’t been used for a number of days. Over time, the resin can separate with heavier material sinking to the bottom and lighter material rising to the top which will affect the ratio and final potting weights.
- Ensure that you have pre-filled the container tanks and allowed sufficient time for the resin material to heat to its optimum temperature before starting the process.
- Create sample batches and allow these to fully set before each production run. The samples can be heated in an oven to speed up the curing process if needed but always allow the samples to fully cool and then use a hardness tester to ensure that you have achieved the correct result.
- Create and implement a work instruction which details set up instructions and the desired measurements.
- Carry out daily checks against this work instruction to ensure all measurements are correct and the process is in control.
So there you have it: some of the more critical factors to be aware of in order to consistently achieve the "perfect pot"!