High Performance Adhesives for Bonding to Liquid Crystal Polymer (LCP) in The Assembly of Electronic Devices

Smaller, Lighter, Faster:

The large consumer electronic device OEM’s are constantly striving to deliver higher device performance and functionality but also provide a robust product that is highly reliable. In addition there is a consumer requirement that electronic devices such as cell phones, watches etc… both look good and are comfortable to hold and use.

These requirements have led OEM’s to design devices that prioritize the use of plastics instead of heavy and bulkier materials such as ceramics, metals. The plastics selected must provide excellent properties critical to the device performance e.g. structural strength, good temperature stability and chemical resistance. One class of plastic that is seeing increased use in electronics applications is Liquid Crystal Polymer (LCP).

Why LCP is Used in Electronic Assemblies:

LCP is becoming a frequently selected plastic in the use of electronic device assembly due to its numerous benefits. LCP is a generic name for a group of high performance polymers that are formed of rigid self aligning molecules. LCP is able to be easily molded into stiff rigid structures that have high dimensional stability at tight manufacturing tolerances. In addition LCP can be molded into structures containing fine detail which are often a requirement in complex electronic component assembly. Another attractive benefit when using LCP is that it has excellent dielectric properties e.g. low dielectric loss, making it an ideal material for use in flexible printed circuits (FPC), Antenna substrates and housings. LCP’s are also chemically stable with good resistance to environmental factors such as heat and moisture.

Usage of LCP in Camera Module Assembly:

One area that LCP is seeing increased usage is in the assembly of Compact Camera Modules (CCM) used in consumer electronics devices such as cell phones and tablets, specifically as the plastic used for the barrel assembly which needs to be bonded to the camera lens. Plastics used in the construction of the camera module are required to be manufactured to high precision and be highly durable to ensure high accuracy when aligning the lens during production and throughout the lifetime of camera module itself. LCP is able to provide CCM manufacturer these inherent benefits and is why its use is becoming more wide spread.

Challenges of Adhesive Bonding to LCP:

Because LCP is a generic term for liquid crystal polymers the actual composition varies depending on grade or supplier. LCP’s contain both crystalline and amorphous phases and these different phases are present in different ratios depending on the specific characteristics targeted by a specific manufacturer. Also LCP manufacturers will often incorporate fillers into the structure as a way of controlling the Coefficient of thermal expansion (CTE). As such LCP surfaces can vary significantly between different grades from the same supplier or from supplier to supplier. In addition to the variation between grades and suppliers LCP’s are often difficult to bond to as a result of their chemical structures and post mold ‘surface skin’ that often forms as a result of the molding process, resulting in a non-polar, smooth surface finish.

All of this creates challenges when using an adhesive to bond the camera module lens to the LCP barrel. In addition as the industry moves away from threaded barrels to thread-less barrel’s the challenges to achieving good adhesion to the LCP further increase as a result of less mechanical fixturing points.

One common approach to improving the adhesion of the adhesive to the LCP is to use a surface modification technique e.g. Plasma Clean. Plasma’s are excited gas species which when targeted onto a substrate surface can modify the surface enough to allow for a better physical environment for an improved adhesive bond. Unfortunately because plasma cleaning is an additive production process, the positive effects are usually short lived and there are often further negative effects such as increased adhesive bleed it is typically not  considered desirable and often seen as a last resort. 

Adhesive Bonding of Lens to Barrel:

When assembling a Compact Camera Module (CCM) for consumer electronic devices the overall device reliability is paramount and cannot be compromised. One critical component in respect of mobile device reliability is drop or impact performance. Cell phones, tablets, smart watches etc.. are frequently subjected to impact events throughout their usable life and so the assembled components that make up a standard CCM must be able to survive these impact events. When LCP is the barrel plastic used, given its inherently difficult to bond surface characteristics, the challenge becomes even harder. 

When formulating adhesives for applications that require high  impact performance it is normal to target a flexible adhesive product that can more readily absorb the forces created during an impact event. More rigid adhesives don’t dissipate these forces so readily and typically fail at much higher frequency.  Conversely when targeting a  high strength bond, highly cross-linked, rigid adhesive formula’s are typically desired. As such this creates a challenge when bonding to a surface, like LCP, which is difficult to achieve high adhesive strength on but that requires excellent impact performance. These competing requirements are the challenge for adhesive suppliers looking to perform lens to barrel bonding when LCP and other difficult to bond substrates are being used.

KRYLEX KU5100 Series Adhesives:

KU5100 series adhesives are UV curable adhesives designed to have excellent adhesion too difficult to bond to plastics, like LCP, and have exceptional impact performance. The products contain proprietary technology to promote a highly flexible structure while maintaining excellent adhesion. This high flexibility leads to superior performance in impact events and is ideal for use in mobile device assembly. There are currently 3 products in 5100 series that incorporate the proprietary flexibiliser added to the formulation:

  • KU5156: Low viscosity, UV curable Adhesive for Lens to Barrel Bonding
  • KU5172: Higher viscosity, Higher Elongation, version of 5156
  • KU5173: Higher TI, Higher Elongation, Faster/deeper cure version of 5156

KU5156 for Camera Module Lens to Barrel Bonding:

KU5156 is a fast cure, UV curable adhesives with high adhesion to a wide variety of  substrates e.g. plastics, metals and glass. It has optimized dispense rheology to maximize manufacturing efficiencies. The product has excellent adhesion to plastics such as LCP and Polycarbonate (PC), commonly used materials in the assembly of Compact Camera Modules (CCM) but also has excellent reliability performance:

For a further product data and information about KU5100’s or other recent camera product innovations (IR Filter and Active Alignment Adhesives) please contact pgleeson@chemence.com or your local KRYLEX representative.

September 13, 2022