Cyanoacrylate bond line thickness

Considerations also need to be taken with regard to the mechanical performance of the joint and the potential sensitivity the adhesive is to bond-line thickness (BLT). Some adhesives are much more tolerant of BLT than others and can be used within variable tolerances in some instances up to and even greater than 1 mm (e.g., epoxies and polyurethanes) whereas others require very small BLT values/ranges in the order of 20-50 pm (e.g., cyanoacrylates). To ensure that such BLT values can be attained, four strategies can be considered ... 

Slow cure may also be due to a thick bond line (adhesive >0.2 mm). Cyanoacrylates are most suited to applications where the bond line is less than 0.1 mm thick although a cure through a volume up to several mm is possible using UV curing cyanoacrylates. 

The gap between the parts and therefore the thickness of the adhesive film has an important bearing on the characteristics of the joint [4], A thick bond line (>0.25 mm) will generally be a weakening feature for cyanoacrylates as the mechanical strength of the cured cyanoacrylate film is likely to be less than the plastic or other substrate... 

---