Adhesives that withstand reflow soldering
In today’s world, electrical engineers are charged with the challenging task of precisely filling an already densely populated PCB with even more components. Environmental regulations that have driven the industry to lead free technologies have added even more frustration to the mix. Solder temperatures increased from 183 deg C to 217 deg C with certain parts of the board seeing even higher numbers. Not only was the temperature increase extreme for the individual components, it also created issues with the parts moving from the original placement of the board itself.
Adhesives have long been used to attach SMD’s to through-hole board as they travel through the reflow oven. On the other hand, manufacturing utilizing re-flow ovens incorporated the thixotropic/green strength of the flux and solder paste mix. Many times these boards are double sided and require an adhesive to hold the parts in place on the bottom of the board as the top side is reflowed first.
Adhesives chemistries have developed alongside the rigid demands of the electronics industry to help alleviate some of the stresses caused by the new heat exposure, heat generation of the parts themselves and even drop shock of the end product as the demand for hand held devices grows. Permabond has developed products to make engineers lives a little easier. Not only can adhesives be used to hold SMD’s in place our products can also:
- Provide strain relieve on the solder joint.
- Act as an underfill to protect the component from stresses caused by physical drops and/or thermal contraction and expansion.
- Be thermally conductive to transfer heat from the SMD onto a heat sink
- Be electrically conductive to attach components that would be damaged during the heat required for soldering.
- Fully encapsulate and entire board or just an SMD to protect it from environmental factors such as moisture and chemical exposure
- Tack down wires to prevent stresses imposed on the part.
- Provide electrical insulating properties to the SMD.
During the course of engineering a board, certain questions need to be addressed in order to choose the right material:
- How will I cure the adhesive?
- How fast and how hot?
- Will the adhesive cure during the soldering process?
- Any shadow areas the light won’t reach?
- Any UV tracers for inspection?
- Two Component
- How much working time do I need?
- How long until the parts sets so I can move it?
- Do I need it to be thermally conductive?
- How much heat do I need to dissipate?
- Do I need electrical conductivity?
- How conductive do I need it and so does the cost of a silver filled material justify the cost
- Do I need the adhesive to be insulating?
- Do I need the adhesive to protect component from chemicals?
- Do I need a hard adhesive or a soft adhesive?
- Does the adhesive need to hold down the part prior to curing (Green Strength)?
- Should the adhesive flow to fill any gaps?
- Can the adhesive meet the temperatures of the wave solder or reflow oven for the duration of the process time?
Permabond offers a broad spectrum of adhesive to match with these requirements and also offers a customising service for bespoke formulations. For further help and advice, please contact Permabond.