September, 2019


www.us- tech.com


Mitigating ESD Risk in Barcode Labeling and Masking Continued from previous page


charge. To eliminate this charge buildup, there are several techniques that can be employed:


l Matching chemistries. By using an adhesive


and release liner that are chemically similar and also closer on the triboelectric series of materials, charge buildup can be decreased. While this is theoretically possible, it is difficult to find a sys- tem that is chemically similar and will function effectively.


l Conductive fillers. By adding conductive fillers


to an adhesive, charges will move through a con- ductive path in the adhesive to ground. As charges develop when the liner is removed, the charge is removed from the surface of the adhe- sive. The concern with this technology is that applying a conductive adhesive to the PCB may introduce a short or current leakage to any exposed circuits on the PCB or com- ponent.


l Electric field shielding. When the


liner is removed from the adhesive, the resulting charge buildup on the adhesive and liner produces an elec- tric field that surrounds the charge. If shielding is applied in the proxim- ity of the separation process, the charge will be reduced. The chal- lenge with this technology is that adding shielding may not be physi- cally possible.


When these types of features are


employed in labels and tapes, the resulting reduction in charge buildup on the adhesive can be significant. A common measurement method of this charge buildup is to use a contact voltmeter to measure the voltage level directly on the charged surface.


Static-Dissipative Label Face. After the label or tape is applied to the surface of a PCB, the insulative face can become a location for charge buildup, especially when handled or contacted by conveyors, etc. A way to prevent this is to make sure charge movement is allowed over the sur- face of the tape or label to a ground point. The charge movement should not be fast, but gradual to avoid a large electric current being intro- duced to the PCB. The standard test method for


measuring charge movement or dissi- pation is ANSI ESD STM11.11. In this method, surfaces are character- ized by the speed at which charges move across them: conductive (rapid), dissipative (slow), or insulative (min- imal/none). If a charge is placed on an insu-


lative surface, it will create an imme- diate high charge density at the point of contact and that charge will have minimal decay over time. If an equal charge is placed on a conductive sur- face, it will not produce a high charge density because of its rapid dissipa- tion across the surface through elec- trical conduction. This rapid move- ment of charge can cause damage to static-sensitive devices if the current exceeds design limits. On a dissipa- tive surface, the charge density will be initially lower than on the insula- tive surface and immediately begin to dissipate slowly across the surface. The dissipation speed helps prevent both high charge densities and rapid discharges, safely neutralizing the charge. The rate of charge movement is


important. A rapid static discharge can be extremely destructive, causing a loss of material or chemical degra- dation at the point of charge. A rapid charge movement can also cause degradation of a circuit. Gates (switches) used in diodes or transis- tors can be damaged by exposure to


high voltages, reverse voltages, high current or reverse current. This is often called electrical over- stress (EOS). ESD is a major threat to meeting short- and


Page 71


long-term performance and reliability require- ments of an electronic device. For device manufac- turing, and especially during PCB assembly, a robust ESD control plan is an absolute require- ment in order to mitigate the risk of ESD failures. A key element of a successful ESD control


plan is to manage the use of charged insulators (e.g. plastics) inside the production environment. Barcode labels and masking tapes are widely used for tracking and protection of electronic devices and are two common charged insulators. The risk of ESD can be reduced by using low-charging and static-dissipative label and tape constructions. Contact: Polyonics, 28 Industrial Park Drive,


Peel voltages for adhesive on a tape and label with and without low-charging features.


Westmoreland, NH 03467 % 603-352-1415 E-mail: info@polyonics.com Web: www.polyonics.com r


See at PCB West, Booth 208


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