dual cure adhesives for precision alignment

Dual cure adhesives for Precision alignment

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.

Prop­er­tiesOS 5101Units
Thixotrop­ic Index1,5-
CTE a120ppm/°C
CTE a256ppm/°C
Glass Tran­si­tion Temp (Tg)137°C
Vol­ume shrinkage1%
Mod­u­lus @25°C13,490MPa

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.

About George Kountardas

George is a Jack of all trades with an unappeasable inquiring mind. Obsessed with new products and technologies, he is always pushing forward for better, faster and more efficient applications. Always learning something new.

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