February, 2013
www.us-tech.com Selective Conformal Coating
devices and modules. As the process increases the durability of electronics that are subjected to various end-use environmental conditions, it adds value to the product. While it does add value, consumers and manufac- turers expect the electronics to work when subjected to dirt, humidity, moisture, corrosive materials, and various other contaminants. This expectation results in a drive to min- imize the cost of the conformal coat- ing process. The lowest cost of owner- ship for this process is achieved by utilizing automated selective confor- mal coating equipment. Selective coating equipment — in
C
contrast to broadcast spraying or dip- ping that require masking — only
Conformal coating is not a one-size-fits-all process; there are “keep-out” zones — areas where coating is not applied.
coats those regions of the board that need coating. The use of properly char- acterized automated equipment is a reliable way to increase yield, increase throughput, and reduce the cost of the conformal coating process. The cost can be further reduced and the speed increased through understanding the capabilities of the selective coating equipment and including those consid- erations at the design phase. The conformal coating process
provides surface level protection to the printed circuit assembly (PCA) and does not cover the entire circuit board; there are areas where coating is not applied, commonly referenced as “keep-out” zones. The coating pre- vents the circuitry from having a reduction in the surface insulation resistance that can cause shorts, arc- ing, and signal cross-transmissions. Because conformal coating is an elec- trically insulating material, it is not applied to areas where electrical con- tacts or connections are needed for the lifetime of the product — such as test points and socket connectors. The coating also inhibits mechanical motion once it has cured, so it is not applied to mounting points, poten- tiometers, MEMS, or devices that are designed with a required motion component. Finally, because it is a coating, there are areas of the board where it is not applied because it affects the optical performance, as with displays and bar codes.
Selective Coating Coating is applied selectively to
the board, either through automated selective coating equipment or a masking process that is subsequent- ly removed after cure. For moderate- to-high-volume production, the low- est process cost of ownership comes when the coating is applied selective- ly through automated equipment. The masking process is done either through mechanical masks that cre- ate shadowed areas or by applying a masking material to the board and removing it after coating. Both of these have drawbacks to the process. Mechanical masks, commonly de - signed into a fixture, need to be cleaned frequently to remove buildup and still leave an area in the shaded
See us at IPC/APEX Booth 1327
onformal coating is an en - abling process that allows for the ruggedizing of electronic
By Brad Perkins, Nordson ASYMTEK, Carlsbad, CA
region where low viscosity coatings must be prevented from flowing into the keep-out zones. In the case of masking material that is applied to the keep-out zones, there is zero value-add to the final product be - cause it is removed after the coating is cured. Masking adds labor and material costs to the bill of materials (BOM) without adding value to the final product. In contrast, selective conformal coating equipment applies coating only where it is needed. This eliminates the need for labor to mask and de-mask as well as the cost of the masking material itself. A complex board can require 3-10 minutes for the mask/de-mask process. The labor
Selective conformal coating system. Continued on page 59
Page 57
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 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136