February, 2013
www.us-tech.com Selective Conformal Coating Continued from page 59
cross contamination to other process- es, and ventilation of the vapors. The cure mechanism is deter-
mined by the materials as well, be they acrylics, urethanes, silicones, or epoxies. The time to cure is related to the material itself, and automated equipment selection depends on the cure mechanisms of the specific material. To minimize the time to cure and the associated work in process as well as line length, design- ers need to look at the specific coat- ings and not the equipment. A high reliability coating
process occurs most efficiently when there is characterization of the equipment prior to introducing the final product. The equipment used to apply the conformal coating has numerous input parameters to opti- mize the process; some of the most critical are the applicator selection, nozzle orifice size, the pressure that causes the fluid to flow, the trans- versing speed of the applicator, height of the applicator from the sub- strate, and the overlap of each pass. The outputs of these variable set- tings provide the coating thickness, repeatability, throughput, and defects, such as bubbles and voids.
Curing the Coating The equipment used to cure the
coating material also has input vari- ables depending on the cure mecha- nism. For thermal cure materials these are typically the temperature of the oven, belt speed, temperature ramps, and for some materials, the humidity inside the oven. For UV cure materials variables are the height of the UV lamp and the speed the board passes through the oven. The output of these variable settings, in conjunction with the material thickness, provides the throughput of the cured product as well as defects, such as incomplete cure or over cure defects. Through first characterizing the
equipment capabilities, the manufac- turer is able to best develop a high yield, maximum throughput process for the end product. There are vari- ables associated with coating a specif- ic board due to board topography, keep-out areas, surface wetting, cleanliness, moisture retention, and component placement. Decoupling the equipment characterization from the final product enables higher reliabili- ty coating processes in a shorter and less costly development timeframe. The timeframe is shorter because it is a simpler process without confound- ing variables, and less costly because of engineering time-savings as well as reduced potential scrap product gen- erated in process development. Each coating material has slightly different rheological characteristics. Under - standing how those interact with the equipment input variables subse- quently provides the best manufac- turing processes. The majority of manufacturers
who have successful coating opera- tions manufacture more than one product. With multiple products, there is a need to develop a process that works with many different selectivity requirements. By initially developing a coating process that is end-product independent, it allows companies to introduce new products more quickly because each product is not a unique project. Finally, the conformal coating
process is a very dynamic process because there are many tolerances that are inherent in it. Some of these are associated with the acceptable lim- its of material viscosity variations, substrate surface energy affecting wetability, surface cleanliness, fixture tolerances, and the coating equip- ment’s own tolerances on volumetric dispensing. All of these processes can be characterized for high yield; howev- er, it is advantageous to have a basic characterization process that can be referenced so as to provide a standard to work from. The equipment can be selected to have closed-loop heaters to control the viscosity, software-con- trolled pressure regulators to dynami- cally adjust the spray patterns based
on closed-loop monitoring, fiducial recognition for increased placement accuracy, bar code scanners for auto- mated program selection, and many additional options as defined by the process requirements. Characterizing the equipment
before introducing the final product also helps to ensure that the initial process is defined in the center of the process window, allowing for the widest range of variation, which is much easier to do when it is defined outside of a specific product. It also decouples trouble-shooting issues from the incoming product (upstream issues) or issues with the coating process itself. This understanding minimizes
Page 61
the need for process support and increases the number of good parts being produced per shift. Automated selective coating equipment is very reliable and designed to run in 24/7 environments; the challenges are with the process itself. It’s important to con- sider the need for and type of coating at the design phase, and properly characterize the equipment. This will help ensure that the product can be manufactured utilizing automated equipment and at the lowest cost. Contact: Nordson ASYMTEK,
2762 Loker Ave. West, Carlsbad, CA 92010 % 800-279-6835 or 760-431- 1919 fax: 760-431-2678 E-mail:
info@nordsonasymtek.com Web:
www.nordsonasymtek.com r
See at IPC/APEX Booth #3115.
4000Plus Micro Materials Testing
The Nordson DAGE 4000Plus delivers a wide range of new features that enable it to be used for micro materials testing
The 4000Plus test platform with Paragon™ software builds on the strong Nordson DAGE tradition and reputation of handling and testing at low geometries.
The 4000Plus offers a wide range of optical solutions for positioning, viewing, recording tests and failure modes, making it the perfect choice where a more comprehensive materials test tool is required.
Application Specific Tooling Nordson DAGE has over 50 years of micro testing experience and continues to evolve test methods. An extensive range of standard and custom tools are available.
www.nordsondage.com |
globalsales@nordsondage.com See us at Electronics West/MDM Booth 3113 and IPC/APEX Booth 2915
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