Dual cure UV adhesives are materials that require two curing methods to fully cure. Either UV and Heat, Moisture and heat or other combinations, these adhesives are designed for specific, challenging applications that require multiple process steps.
Optical alignment is one of the most common use for them. They are designed to precisely align optical components and facilitate maximum optical signal strength through low shrinkage, low coefficient of thermal expansion (CTE) and high integrity light transmittance.
Active alignment process
Active alignment is when we are using the advantages of dual-cure to align the optical path of sensors, fibers and other light path critical devices.
The problem starts with the lens & barrel manufacturing tolerances as well as the optical sensor and fiber placement tolerances. These are causing the light path to be off-centered and the device to either malfunction or not function optimally. Even though the lens and sensor look to be perfectly aligned, the light path is off route.
In order to solve this we introduced the active alignment process during the device assembly. The usual process for such bonding starts with dispensing the adhesive and then positioning and aligning the component. Next steps usually consist of fixating the component with light cure that is then finalized with Heat curing. Hence the need for dual curing. It is not necessary but it is process dependent and can help with the precision alignment steps.
You can see a quick description of a CMOS sensor bonding process in the following image:
This is not limited to lenses but it is indicative of the process. We dispense the adhesive, attach and align the path, flash with UV light and then move the heat oven. This is also something common for optical fiber path calibration. When dealing with optical switches, dual-cure adhesives aid to:
- Precisely bond the assembly along the light path,
- Deliver high bond strength
- Provide superior dimensional stability
- Minimize shrinkage to ensure lens to fiber signal optimization
Key requirements for adhesives that can be used in sensor bonding and optical switch precision alignment are:
- Adhesion to variety of substrates (PC, LCP, etc.)
- Low temperature cure – below 100°C
- Fast cure – below 60mins
- Operating temperature range -40ºC to 130ºC
- Low halogen content
- Dual curing – Combination of heat and UV cure
UV Cure strengths and limitations
As you would expect, UV curing doesn’t only come with strengths and advantages. It is a great and fast tool in our disposal but it comes with specific limitations as well.
Their main strength is that they cure fast and “on-demand” at room temperature to facilitate part alignment. These one-component materials contain no solvent at all and consume less space and energy. Their fast throughput ensures that there are minimal work in progress components and that things move fast, aligned and efficiently.
On the limitation side, Oxygen inhibition and shadow area curing can prove to be an issue. Cure is sensitive to light with special conditions and a direct line of sight cure. Shadowed areas will always require a heat cure step while filler CTE can also be problematic
Dual cure adhesives such as LOCTITE STYCAST OS 5101 are used for optimal, precise optical lens and component alignment during the in-line assembly process. They provide excellent alignment accuracy for maximum light transmission in high-speed optical transport network solutions. They are ideal for many optical applications including PEI lens active alignment and bonding, OSA to TO-CAN pre-fix, silicon photonics assembly and passive component assembly such as collimator lens bonding.
| Properties | OS 5101 | Units |
| Viscosity | 22,000 | mPas |
| Thixotropic Index | 1,5 | – |
| CTE a1 | 20 | ppm/°C |
| CTE a2 | 56 | ppm/°C |
| Glass Transition Temp (Tg) | 137 | °C |
| Volume shrinkage | 1 | % |
| Modulus @25°C | 13,490 | MPa |
| Outgassing | 0.6 | % |
| Cure | See | – |
We offer a wide range of Dual cure adhesives such as LOCTITE 3217, ABLESTIK NCA2286, ECCOBOND 3707 and other electronics assembly adhesives. Even though we have a comprehensive list of proven materials there are also many other solutions up our sleeve that are not public yet.
Do you need something for your Photonics assembly, optical switches, cameras, sensors, lens, or any other optical bond? Please contact us and we’ll help you choose the best product for your application.
