A prevalent method for testing the bond strength of dies and other components that have a large area to thickness ratio is known as stud-pull. Often the stud is attached to the top of the component to be pulled using superglue (cyanoacrylate); a moisture curing glue that can bond to most surfaces. Nordson DAGE has had remarkable success using Loctite 480, which is a version strengthened with rubber particles. One of the significant issues with using superglue is that it requires several hours of waiting for it to cure to full strength. This is because moisture is needed during the curing process and if moisture cannot pass through the components being bonded (such as a silicon die and aluminum stud), then the moisture can only enter via the outer edges of the bonded surface.
New UV Adhesive
UV curing glues are a different class of products. When exposed to ultraviolet light, UV glues tend to cure rapidly and overcome the issue with moisture ingress. Loctite AA 358 UV curing adhesive was used to glue nylon M2 bolts, with a head diameter of 3.7 mm, to square silicon die surface. For effective use of the UV curing glue, the stud must be transparent to UV light, hence replacing the aluminum stud with one made of nylon (Figure 1). The bolts were positioned on top of the dies, using a small spot of adhesive, with no pressure applied during curing. Over the course of six minutes, a 4 Watt UV (type 3) curing lamp was used to cure the adhesive, before stud-pull testing.
Figure 1. Nylon stud being bonded to a silicon die curing under a UV lamp.
Comparably, Loctite 480 superglue was used to glue steel M2 bolts to another set of identical silicon dies, with a curing time of three hours. Using emery paper (silicon carbide), all the bolt heads and the die surfaces were then abraded before bonding to provide the maximum strength.
To test the bond strength, a 4000Plus, fitted with a PP50KGHR cartridge and using Paragon™ Materials software control, was used. Bonding the silicon die samples to a block of aluminum, they were then clamped into a standard work holder vice and using an M2 threaded female stud-pulling fixture to pull the stud. A typical force vs. axis displacement result is shown in Figure 2.
Figure 2. Pull test results of UV Glue/ Nylon studs.
Altogether, five samples of UV glue/Nylon and five samples of super glue/steel were tested (see table). The mean load to failure of the standard superglue was a 5.6 kg force, while that of the UV glue was a 5.2 kg force. Both glues failed at the point between the adhesive layer and the bolt head. Therefore, they both remain well-fixed to the silicon surface and the nylon bolt threads are robust enough to carry the load of a 5 kg pull test. Although the mean force was lower than that of the superglue, the cure time for the UV glue was vastly improved.
Additionally, nylon countersink bolts could be a very cost-effective stud for small dies instead of the previously machined aluminum studs, proving to be both time and cost-efficient. The nylon could be machined or molded to match the die size if the maximum pull force was required. While high-power UV lamps can often introduce safety issues, a low-power cosmetics lamp designed for home use was used during these tests, so the additional equipment can be cheap, safe, and easy to use. Alternatively, Loctite offers the Zeta® 7401 Flood System, desktop UV curing station, specifically built with these tasks in mind, inclusive of a 400-Watt bulb that can rapidly cure the adhesive.
|Glue/steel Stud Pull Load (kg)
|Glue/nylon Stud Pull Load (kg)
New, rapid cure adhesive
|Time to cure 3 hours
||Time to cure 6 minutes
- UV adhesives can be used instead of conventional superglue for silicon die stud-pull
- The stud must be transparent to UV light such as unfilled nylon
- The bond strength was only slightly less than the superglue
- Loctite AA358 was used successfully
- The cure time can be reduced from hours to minutes using UV glue
This information has been sourced, reviewed and adapted from materials provided by Nordson DAGE.
For more information on this source, please visit Nordson DAGE.