Adhesives for Optical Assembly Applications

Interview conducted by Stuart MilneMay 20 2015

Rohit Ramnath, Application Engineer at Master Bond, talks to AZoM about optical adhesives and the benefits of using their EP42HT-2LTE epoxy.

Could you please provide a brief introduction to the industry that Master Bond works within and outline the key drivers?

Master Bond prides itself in custom formulations providing specific performance properties designed for unique applications. These compounds exhibit the most advanced properties required for a number of different industries, including the aerospace, medical, optical, electrical, electronic and other manufacturing industries. The key driver for developing new products is to closely work with engineers, right from the design & prototype phase right to the stage of production.

Could you give some examples of bonding applications in optical assemblies?

In a broad sense, optical assemblies requiring adhesives can be classified into two main categories:

• a. Applications requiring an optically clear adhesive: In such cases, optical properties such as transmission at various wavelengths and index of refraction play a vital role. Some examples include: bonding glass lenses or glass to acrylic/polycarbonate.
• b. Applications where optical clarity is not required: In such cases, the adhesive can even be opaque. Some examples include: bonding glass to aluminium for a mirror assembly or stainless steel to ceramic to name a few.

What are some of the important parameters that one must keep in mind while selecting an adhesive for such optical assemblies?

Having broadly classified the two main types of applications in optical assemblies, it must be noted that while optical clarity is usually important, engineers must also be mindful of other properties such as low outgassing, low shrinkage, and dimensional stability.

In one of your recent case studies, a customer was looking for an adhesive with low shrinkage and low CTE, as they were using glass and ceramic based substrates. Can you explain the importance of low CTE in such applications?

Basically, both glass and ceramic have an extremely low CTE, and the customer was looking for an adhesive, which would offer high stiffness/rigidity, close match to the CTE of the substrates, and precise alignment post cure. A filled, low CTE adhesive would meet such requirements, and offer superb dimensional stability.  These are some of the reasons to prefer a low CTE in such applications.

What makes your epoxy, the EP42HT-2LTE, a good option for use in bonding applications in optical devices?

EP42HT-2LTE offers very rigid, dimensionally stable bonds, with an extremely low CTE (~9-12 ppm/C) thereby, offering precise alignment capabilities. Also, it is capable of maintaining this alignment during temperature fluctuation through a wide temperature range. In addition, it passes the NASA low outgassing specifications, which might be vital in some sensitive optical devices. Finally, since the EP42HT-2LTE is a paste, it is a good fit for optical applications where minimal flow during the application and curing process is required.

What problems do your customers typically face in this area, and how are these issues solved?

There are many challenges while selecting the right adhesive for optical assemblies. We will try and describe a couple of scenarios here:

• In applications where precise alignment post cure is very important, typically, rigid curing, dimensionally stable adhesives are used. Adhesives with very low CTEs can provide these properties.
• On the other hand, there are applications, where low or minimal stress needs to be imparted on the substrates from the adhesive. In such cases, adhesives which provide a good degree of flexibility are used.

In both cases, there might be a need for an optically clear system with specific refractive index and transmission requirements. There are optically clear adhesives which can cure rigid or flexible, and depending on the other requirements, engineers must select the appropriate compound.

Where do you currently supply to? Are there plans to expand operations in the near future?

Master Bond’s compounds are shipped directly from our state of the art manufacturing facility to customers worldwide. There is a constant drive to formulate new compounds, expand operations to meet diverse demands from customers, while providing consistent and excellent customer service, as well as technical support.

Where can our readers learn more?

They can learn more by clicking here.

About Rohit Ramnath

Rohit Ramnath is an Application Engineer for Master Bond Inc., a custom formulated adhesives manufacturer. He analyzes application oriented issues and provides product solutions for companies in the aerospace, electronics, medical, optical and oil/chemical industries. He graduated from Carnegie Mellon University with a Masters Degree in Chemical Engineering, where he wrote his thesis on analyzing drilling fluid emulsions for enhanced oil recovery.