September, 2016
www.us-
tech.com
Page 59
Dual Applicators Improve High-Volume Non-Atomized Coating
By Camille Sybert and Michael Szuch, Nordson ASYMTEK
mist. Non-atomized coating, or selective coating, controls the coating material’s dispense shape while maintaining its original liquid form. Selective coating only covers specific components or areas of a board while respecting keep-out zones. It has the potential to increase transfer effi- ciency, selectivity, throughput, yield, and reduce masking and rework. The goal in high-volume manufacturing is to
A
optimize the dispensing setup to improve dispense quality, process control, reliability, and repeatability — while reducing material costs. To achieve high-qual- ity, accurate, repeatable coating with efficient throughput, non-atomized coating is often used.
Non-Atomized Coating Methods Non-atomized dispensing meth-
ods include film coating, needle dis- pensing and jetting. Each of these works well with solvent-based mate- rials, which are used to improve transfer efficiency, selectivity, and throughput. Typical cured thicknesses for
solvent-based acrylics and urethanes are 25 to 75 µm (1 to 3 mils) in a sin- gle pass. Thickness is specified by IPC standards and can be controlled
tomized spray is currently the most common method for applying conformal coating and works by dispersing material into a fine
sweep across the board at speeds up to 750 mm/s (29.53 in/s). The film coater does have a few restrictions.
Film or curtain coater tip and spray pattern (left), final pattern (right).
The applicator is limited to solvent-based materi- als with an optimized viscosity. While selective, the film coater still dispenses large volumes of material. Low-viscosity material may pool around leads and other components, thinning coverage in other areas. The movement of the fluid flow is sub- ject to the material’s properties and to the surface tension of the board. Due to the applicator’s physi- cal size, access around tall components is limited. Continued on page 61
Needle applicator tip and
coating pattern (left), final pattern (right).
by hardware, line speed and viscosi- ty. The amount of solvent added to the solvent-based material creates the desired thickness. Non-atomized coating methods
mold the fluid shape to obtain selec- tivity, clean edge definition, and ensure desired dispense volumes. They provide a higher wet-dispense accuracy without overspray. While all three methods are selective, they each provide a different degree of selectivity, so complex boards can often benefit from using a combina- tion of these applicators.
Film Coating A film coater dispenses in two
distinct shapes. The primary shape is a leaf pattern made with a cross-cut nozzle that dispenses a curtain of material as the applicator moves. At a perpendicular angle, the dispense pattern is a knife edge that sets the pass edge on the substrate. Dispense pass widths can range
from 3 to 15 mm (0.12 to 0.59 in.), though typical dispense passes are approximately 10 to 12 mm (0.39 to 0.47 in.) wide. The shape enables the placement of significant quantities of fluid in broad, wide passes that are suitable for low-profile, surface mount populated boards. With low components, the applicator can
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116