Q&A’s: How to Save on Assembly Bonding Processes…
March 17th, 2009
DYMAX recently had a webinar informing people how to save 30% on their assembly bonding process. We talked about real-life ways to optimize assembly processes with cure-on-demand UV/Visible light-curable adhesives. This archived webinar is now available for viewing.
A lot of questions were asked during the webinar session. I decided to post a few below. Some of you may have the same questions in mind.
| Question | Answer |
|---|---|
| Can UV lights be added onto an XYZ robotic arm? Are they compatible with the software systems? | Light sources can be mounted and used with many XYZ systems and integrated seamlessly into the software controls. Some systems offer the ability to dispense a bead or gasket and then follow the bead or gasket with the end of a lightguide from a high-intensity spot lamp system. |
| What thicknesses can the light-curable materials be used to? | Typically, applications with a thickness of <0.25 inches are common. Best bond line thicknesses are usually 0.002-0.006 inches (0.05-0.15 mm), conformal coatings are typically 0.001-0.003 inches, and some special deep-section potting can be over 0.25 inches. |
| How heat resistant are the light-cure materials? | This varies by product, but most will be in the 200-400°F temperature range. |
| Most processes are validated/established processes. How much costs have you seen associated with an initial implementation of a UV-curing system? | This depends on the lamp type and application. Some starter R&D and low-production lamps start in the $2,500 range while other lamps with conveyors or XYZ tables can be much more. DYMAX offers a Trial Rental/Lease lamp program with 2 weeks free for trials and evaluations. |
| Can you explain See-Cure technology again? What are other methods to check cure quality? | See-Cure Technology utilizes a dye that loses its color with the light energy (intensity and time exposure). The color goes from blue to clear upon cure. Once the material is clear, it will remain clear, and be aesthetically pleasing to the eye. Other methods to check the state of cure is by either mechanical testing (such as tensile strength, durometer, and pull to destruction), or by chemical analytical testing (such as gas chromatograph on an extract sample, or FTIR of the cured material) |
| You mentioned “potting”. Can you please expand on? What is the maximum depth of the potting? Can you cover moisture cure technology? | Potting is typically filling a small well or dam with adhesive to protect components, circuits, or seal a housing/port. The viscosity of the adhesive/coating is low so that it self levels, and fills the cavity. Typical maximum depth of potting applications are <0.25 inches, but some special 2-part light-curable adhesives can be mixed to get a chemical reaction at deeper sections, while still allowing the benefit of a light-curable adhesive to lock in and seal the top surface. Moisture cure technology allows areas that can’t see UV/visible light to be cured with atmospheric moisture in the air, and takes a few hours to complete the cure. |
| What kinds of eye protection do you need when implementing UV-curable materials? | DYMAX recommends that lights be fixtured to point away from the operators to avoid direct exposure. We provide tinted goggles that meet current ANSI standards, and some customers create custom shielding using brown PVC shielding or smoked/tinted polycarbonate sheet. We also provide training to operators as needed. |
| Will any of your adhesives continue to cure after the UV light has been removed? | Some types of hybrid systems with moisture cure technology may continue to cure after the UV light has been removed. Some UV light-curable epoxies continue to harden slightly if they have achieved 90% of full cure, but extra care must be taken when working with these materials. |
| Are any of the light-curable materials RF & microwave frequency “friendly”? | Yes. Certain formulations are compatible with RF and microwave frequencies, and are transparent to these wavelengths. |
| Is there any concern, other than cosmetic appearance, when yellowing of the cured media occurs? In other words, is there cure quality issues if yellowing occurs? | Usually yellowing is a cosmetic phenomenon, with little impact on physical properties. Some optical applications do have a problem with yellowing as it would change the optical transmission of light through the adhesive. Therefore, an optically clear adhesive designed to be non-yellowing may be a good choice in this situation. |
| Can you overcure? Does the adhesive break-down? | It is more difficult to overcure these acrylic-based light-cure adhesives. They are very forgiving, and it would have to be an extreme case of overcuring. However, I have seen a few cases where engineers put an adhesive under a static light source and went to lunch. Upon return, the adhesive had too much UV light at high intensity with too much resultant heat, and started to break down. |
| Do you recommend specific fillers that will not hinder the cure process? | There are a number of fillers available on the market which do not hinder the cure process. Selecting the proper filler that yields a clear or translucent adhesive is a trick that the chemists use as they formulate. |
| Can you affect durometer with level of cure? | If you plot durometer versus cure time with a constant intensity, you would actually see the durometer level off and plateau. Over-exposing the adhesive to 2x, 3x, 4x cure times do not usually have a negative effect. |
| What, if any, surface preparation is required to optimize the effectiveness of these adhesives? | On some difficult to bond to substrates like PE and PP, surface preparation can improve the adhesion. Chemical primers, corona treatment, or plasma treatment (preferably with oxygen gas) are very commonly explored, as well as UV pretreatment of the surface. |
| How do you clean up “bleed out” or excess material? | Removal of uncured adhesive after application can be done with a foam wipe, cloth, or cotton swab, followed with an alcohol wipe (isopropanol, methanol, or other organic solvent). We do have a technical bulletin available with suggestions on how to clean up both cured and uncured adhesive residue. |
| I have heard that pre-exposing the substrate to UV light has a similar effect to surface treatment. Can you comment on this? | Pre-exposing a low-surface-energy plastic or substrate with high energy, short wavelength UV light is one effective way to increase adhesion, similar to other surface treatment options. |
| What is the pot life of adhesive once dispensed? | As long as the adhesive is kept away from light and dust, it is okay for a long time. We generally recommend short work times since manufacturing environments typically have a little bit of visible light that could start to polymerize the material. Also dust contamination should be avoided. |
| Does the fluorescence of the adhesive change from pre-cure to post-cure? | The fluorescence of the adhesive does not change from pre-cure to post-cure in most cases. |
| What packaging is available? | We offer a number of different package sizes, from 3, 10, 30 mL syringes, 170, 300, 600 mL cartridges, L or kg bottles, 15 L pails, 55 gallon drums, and totes. |
