The number of camera modules used in consumer electronic devices continues to grow aggressively as electronic devices become both more mobile and, increasingly, wearable.  Market estimates predict that total revenue for CCM (Compact Camera Modules) will exceed $35 billion (US) in 2021, rising to nearly $50 Billion (US) by 2025. In addition, the number of Cameras present on or in automotive vehicles will also increase significantly with Automotive camera module volumes predicted to be broadly equivalent to the number used in cell phones by 2025. 

KRYLEX research scientists have developed a full range of adhesives for the assembly of CCMs, leveraging corporate expertise and historical core competency around UV cure and dual-cure adhesive technologies. Depending on the type of CCM device, either fixed or autofocus, these CCM devices can use between 5 – 10 different adhesives in the construction of the final device. As such selection of the adhesive is critical to the final device performance and reliability. Depending on the specific bonding application each adhesive will have very specific performance targets. 

Active Alignment  (AA) Process in Camera Module Assembly:

A general increasing trend in the assembly of camera modules is a growth in the number of lenses being incorporated into the modules. As the number of lenses increases the importance of accurately fixing the correct focus is getting ever more critical. Dual Cure, UV + Heat, and Adhesive solutions are used to fix the correct focus during a production assembly process called Active Alignment (AA).

The adhesive AA assembly process involves a series of production steps. The AA adhesive is dispensed onto the image sensor housing. The lens holder is placed into contact with the dispensed adhesives. The next step is for the image sensor to be powered up and the lens aligned to the correct position for the best image quality capture. Once the perfect image focus is found the assembly equipment applies UV/ Visible light energy to instantly cure the adhesive and fix the correct lens alignment. The UV step provides sufficient strength to fix the camera focus in place correctly and allow the units to be moved and safely transported to the secondary adhesive cure step, box oven curing. The box oven cure step ensures that any remaining uncured portion of the adhesive is cured and all-polymer cross-linking is complete. This heat cure sets the final cured adhesive properties vital for a robust bond that will enable effective and reliable operation of the camera module throughout the device lifetime.  

Epoxy Adhesives for Active Alignment – The Benefits and Challenges

The vast majority of AA adhesives available in the market today are based on epoxy resin chemistry. Epoxy is an ideal choice for a production process that requires both a UV  and heat cure process. Epoxy curing agents are widely available for both UV and heat curing. In addition epoxies, resin adhesives are known for their ability to process easily and also have excellent adhesion to a wide array of different substrates, e.g. plastics, metals, glass while offering excellent environmental stability and reliability. 

Aside from the generic benefits of Epoxy resin, an AA adhesive must often meet specific and varying critical performance criteria on a case-by-case basis. Depending on the specific OEM or camera module device manufactures there are a number of factors that can create specific challenges. 

The use of lightweight, thermoplastic plastic components for the assembly of camera module devices is common. Plastics such as Polycarbonate (PC), Liquid Crystal Polymer (LCP), etc… are widely used because they are light, strong, stiff, have low moisture absorption, and have good chemical resistance. These plastics often have a variety of surface finishes depending on the manufacturer and are often available in a variety of different product grades. This can cause challenges for adhesives because often surfaces will be different enough between manufacturer to manufacturer or product grade to product grade, that adhesion and/ or reliability performance can differ significantly. 

Another consideration is the sensitivity of the plastics components to elevated temperatures, like that seen during a heat curing step. Any subtle change caused by elevated temperature to the plastic could fundamentally change the performance of the device, as such AA adhesive thermal cure steps need to be tightly controlled and typically restricted to no higher than 80◦C. 

Another important consideration to consider for a successful AA process is adhesive volumetric shrinkage. It is common for epoxy adhesives to have relatively high shrinkage e.g. 3-5%, however, if the adhesive shrinks a lot as a function of the adhesive cross-linking process then it is likely that the optimised alignment for perfect image quality will be affected. Shrinkage as a property can also be correlated with cure condition or temperature. When higher temperatures are used to cure the adhesive there is a potential for more shrinkage, whereas at lower temperatures the reverse is true. Therefore being able to effectively cure lower temperatures is beneficial when using heat-sensitive substrates or as a way to help limit negative impacts associated with adhesive shrinkage.  

Another product variable that can disrupt the alignment process is adhesive water absorption. If the cured adhesive absorbs too much moisture during device usage at ambient and elevated temperatures then the adhesive can swell and result in a shift of alignment and reduced image quality.

In addition, Epoxy adhesives used in Active Alignment are typically 1-part or pre-mixed. These pre-mixed formulas are typically highly reactive at Room Temperature (RT) and often require frozen storage at temperatures as low as -40◦C, requiring expensive, high energy usage, industrial freezers. Commonly, with most pre-mixed epoxy adhesives, once thawed the cure reaction begins and means work-life (time the product is stable at RT) on the production floor is often short and dispense performance can become variable over time. Most AA adhesives available today are designed to cure at elevated temperatures of around 80◦C because making the system react more quickly at an even lower temperature than 80◦C, typically results in product worklife being prohibitively short. KRYLEX KURA-LOW Technology addresses the traditional problems associated with 1-part, low-temperature cure epoxy adhesives.

KRYLEX Dual Cure Active Alignment Adhesives Incorporating KURA-LOW Technology

KRYLEX KURA-LOW Technology was developed to enable high product stability at RT but have good product reactivity at temperatures between 60-80◦C. The high product stability at RT enables extended product work-life e.g several weeks. The high product stability at ambient conditions has further benefits effectively eliminating the need for dry ice during shipment and use of high energy consumption -40◦C industrial freezers, potential reducing costs and lowering carbon footprint due to reduced energy consumption.

KRYLEX KD7009 is a AA adhesive that is based on KURA-LOW Technology. The product is able to be cured at temperatures as low as 60◦C but has a very long work life at RT. The product can be stored in refrigerator at -5◦C or in a standard commercial freezer at -20◦C. The UV cure is fast and the depth of UV penetration is high. The product has an optimised, thixotropic rheology, to enable easy, robust dispensing but a high enough thixotropic nature to ensure ‘shape stability’ and minimal unwanted movement post alignment, prior to UV cure. The product has excellent adhesion to both metal (SUS, Al) and plastics (PC, LCP) and excellent reliability performance (Heat & Humidity).

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A full summary of KD7009 performance benefits can be seen below: –

  • No requirement for dry ice shipment.
  • No requirement for -40◦C frozen storage.
  • Long product work-life at ambient temperature
  • Fast UV Cure
  • Oven cure at 60 – 80◦C
  • Low shrinkage
  • Low moisture uptake.
  • Low weight loss
  • High adhesion to metals and plastics
  • High Impact Performance
  • Excellent hot wet stability 85◦C:85% or 60◦C:90%

For further product data and information about KD7009 or other recent camera product innovations (IR Filter and LCP Lens to Barrell bonding) please contact pgleeson@chemence.com or your local KRYLEX representative.