August, 2019
www.us-
tech.com
Designing PCBs for Harsh Environments
Continued from previous page
the top side of the PCB and has a large-enough surface area, a metal heat sink may serve to remove heat from the component by conduction, and thereafter by convection from the surface of the heat sink itself to the colder air surrounding it. Some- times the hot component may be mounted on the underside of the PCB and it may not be possible to mount a heat sink directly on the component. The technique designers usual-
ly follow is to use a large number of heat vias or thermal vias to conduct heat away from the hot component to a copper layer on the top side of the PCB, from where it can be trans- ferred further to a proper heat sink. Traditional options available to
the designer to manage heat from a PCB can be listed as follows: isolat- ing or removing the heat source; re- ducing power density; providing bet- ter cooling mechanisms; increasing the size of the heat sink; using larger conductors; and using exotic dielec- tric materials capable of withstand- ing higher temperatures. All of these impact the weight, size and cost of the entire system. Designers must consider implementing them in the earliest stages of design and concept development.
New Technologies PCB manufacturers are aware
of the limitations of traditional fabri- cation practices. Therefore, they al- ways strive to keep abreast of cur- rent design challenges by offering newer PCB technologies specifically for applications involving higher
temperatures. One of the methods employed is to use heavy copper in their PCBs. This increases the cur- rent carrying capacity, and due to lower resistance, lowers the heat losses. There are different ways to accomplish this. We classify these as heavy cop-
per or extreme copper boards. As the name implies, these boards use heav- ier and thicker copper layers than standard PCBs. However, heavy cop- per is required only for circuits carry- ing higher currents, and a PCB may combine heavy copper and standard copper to allow higher currents and signal currents to be present on a single board. While the same process applies
for fabricating heavy copper PCBs as that required for the regular boards, some special etching and plating techniques apply. Presence of heavy copper has the advantage of lower re- sistance, allowing higher currents to flow at lower heat losses in the con- ductors. This allows designers to in- corporate such features as onboard heat sinks operating at high efficien- cies. This not only reduces product size, but also allows incorporation of onboard planar transformers. Rather than use a thicker cop-
per layer and plating on a PCB, there is another approach, i.e., embedding heavy rectangular copper wires where necessary. While the advan- tages of this technique are the same as that when using heavy copper PCBs, the added advantage is in the fabrication, where special etching and plating requirement is no longer required.
Continued on next page
Page 37
OUR LABELS DON’T TAKE ANY STATIC
Don’t leave the prevention of an electrostatic discharge (ESD) event up to chance. An ESD event in the PCB assembly process can cause physical damage to circuits and result in latent defects and reliability concerns. Protect your most sensitive devices from static arising from both human contact (HBM) and charged devices (CDM) with Polyonics® ESD-Safe polyimide and polyester label materials that meet the requirements of the ANSI/ESD S20.20 standard.
Visit
polyonics.com/feelinglucky for more information and to download our white paper, The Critical Role of an ESD Control Plan in PCB Assembly.
Personal Chemistry
603.352.1415
info@polyonics.com
Top test engineers trust Acculogic to deliver systems for:
Automated Test
Acculogic engineers systems for real production environments. So, you can ship defect-free
products on-time and within budget.
CELEBRATING YEARS
OF INNOVATION & EXCELLENCE 1992-2017
The Scorpion BRiZ
acculogic.com/easy The FLS9xx Platform
Quality
DO YA FEEL LUCKY ESD?
WELL, DO YA?
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
