Preforms for sealing and potting
Original article date: September 1998
An innovative approach to sealing or potting electromechanical components comes from US company Multi-Seals – solid pre-forms that melt when heated to form a seal
Precision epoxy preforms are one-part resins that offer a no mix no mess solution to the problem of sealing and potting small parts such as electromechanical components. Solid at room temperature when heated they melt and cure forming a consistent seal that protects components from dust moisture oil solder flux and conformal coatings. They can withstand high soldering temperatures and all of the most common industrial cleaning solvents.
The heat is applied for a specified time depending on the shape size and material used first to melt then to flow and finally to cure the material which is always an electrical grade epoxy or epoxy-phenolic. This method eliminates mixing and metering of two-part liquid epoxies as well as the viscosity variations that can occur. Available shaped include rings rectangles ovals ellipses and triangles. Custom preforms can also be designed and manufactured to suit specific application requirements.
Best curing results are obtained using a forced convection oven preheated to the appropriate cure temperature. A mechanical convection (air circulating) oven allows for the fastest recovery and the most consistent means of heat transfer. The oven should be calibrated at least once a year.
Typically 150 is a good starting point. Adequate cure for most applications will take between 30 minutes and two hours depending upon the grade. Allowances should be made for oven recovery time and component mass including loading trays.
For production purposes adequate cure schedules should be determined experimentally and then strictly adhered to. This is done by placing thermocouples throughout the oven to determine the effects of component mass. The longest time it takes for any of the thermocouples to reach cure temperature should be added to the listed cure times in the data sheets. Adding an additional 5-10 minutes is also recommended.
Preforms need to be stored in a cool dry area and in closed containers when not in use. An air-conditioned office is best but not absolutely necessary. Refrigeration can cause condensation of improperly handled.
The preforms can be dispensed at rates of 200 to 600 using automatic or semi-automatic equipment though they can of course be applied manually as well. Templates pick and place machines and bowl-fed gravity tracks are all viable loading methods for dispensing epoxy preforms.
- Multi-Seals
- Kenneth Harvill
- 00 1 860 643 7188
September 1998