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Resins: Five Essentials to Achieve the Right Cure

In my previous column, I looked at some of the critical things you need to consider before selecting your resin, which covered hardness, colour, viscosity and cure time. I do hope readers found this simple back-to-basics guide a useful starting point for further study and consultation. Of course, when it comes to the choice and application of resins, there’s a lot of information to take in, and over the following months I hope to distill this and provide some useful tips and design advice that will help you in your quest for reliable circuit protection.

Right, you’ve now chosen your two-part resin and it’s time to mix the components and get to work, so this month I’m going to turn my attention to the all-important job of mixing the resin (Part A, to use the terminology) and hardener (Part B), taking care that you get the ratio right and that you are conducting this critical part of the procedure under the right atmospheric conditions, and with all due regard for safety procedures. Get the mix wrong at this early stage and you will not achieve a satisfactory cure, which will ultimately lead to all sorts of problems later for the product you are potting or encapsulating. Anyway, continuing the five-point guide format that I introduced last month, here are five things to make yourself aware of before you start mixing.

Mix Ratio
Quite possibly the most critical aspect of resin mixing, which will have long term adverse repercussions if you get it wrong! There are two methods of mixing a resin with its associated hardener: by hand or using specialist dispensing equipment. If mixing by hand, then the ratio of the weight of the two components is the more useful method to employ. If mixing using dispensing equipment, then the volume ratio is used. 

If the job is relatively small, then you are likely to use a resin pack, which provides the resin and hardener in precise quantities, in separate compartments of the pack. When you are ready to use the product, you simply remove the clip or other separating device between the compartments and ‘massage’ the resulting pouch, ensuring that both components are completely mixed.

To read this entire article, which appeared in the November 2016 issue of The PCB Design Magazine, click here.