Thermal Risk Management

(TRM) in Electronics

The TRM software is a special tool of engineering analysis which examines the needs and necessary details of PCB simulations. Trace temperatures due to Joule heating (current carrying capacity) and board heating by components are calculated from physical principles but without academic ballast. Because the user is guided through the software in a way a software assistant does, it is perfectly suited for use by a PCB or assembly designer. Neither knowledge about numerical methods or gridding techniques is required nor a need to be coupled to a high-price electronic CAD System.

TRM - Thermal Risk Management

TRM can handle single layers, multilayers, SMD heat sources, embedded components, pins, Inlays, busbars, copper thickness, adhesives, plugged and unplugged, blind and burried vias, heat sinks, chassis parts and bolts. Requirement: the PCB should be more or less geometrically flat. Components, heat sinks, cold plates and cables are characterized by thermal parameters.

For a calculation of current-carrying capacity and temperature the following input data are needed:

  • Layer stack
  • Conductive pattern of all layers, e.g. Gerber
  • Hole pattern of plated and non-plated drills, e.g. Gerber or Excellon
  • Pins to define current input and output and current value (in Amps)
  • Components and the power loss (in Watts)
  • External conditions, e.g. ambient temperature, convection type or air speed.

As results, you get calculated thermal images (x-y resolution down to e.g. 100 mu) of every layer, detailed maps of current density, maps of potential (and potential drop) and maps of temperature dependent material properties and local heating power. You will see whether the trace width is sufficient, you will recognize bottlenecks with high current density, probably ith overheating (or not). In a transient simulation you can set virtual thermal couples and record the temperatures there. Both power loss and current can be defined by their permanent values, or by any time pulses via spread sheet definition. Comparison shows, that simulation and infrared thermographs usually agree within 10% or better.

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Trm1 Trm2

What is TRM?

A PCB has 4 major objectives:

  • to represent the schematic diagram in copper
  • to conduct electrical signals and currents
  • to hold components and connectors
  • to work up to a certain temperature limit.

Points 1 and 2 are done in your layout software (routing, placement), point 3 is done at the end of the manufacturing process in a soldering machine, point 4 depends on the power losses of the components and heating in traces and the external cooling conditions. With TRM do endurance testing of the PCB by using numerical simulation - before starting with a prototype. The goals are to recognize weak spots as early as possible, to tune engineering strategies and to avoid both expensive oversizing and dangerous under sizing. TRM software is calculating temperatures from currents and power losses in a 3D layout and assembly geometry. TRM is a development of ADAM Research, Germany, founded by Dr. J. Adam who has more than 20 years of experience in the field of electronics cooling.

What is needed for a calculation

  • Conductive pattern (e.g. Gerber, e.g. from an ViewMate Pro input)
  • Layer stack (materials and layer thickness)
  • Drill files (e.g. Excellon, e.g. from an ViewMate Pro input) for plated and non-plated vias
  • Pads or pins for input and output currents, plus current value or voltage
  • Power losses of other components
  • Ambient cooling conditions (e.g. air temperature, mounting spots, air speed)

Which results will you get?

  • A calculated thermogram (resolution in x, y ca. 0.1 to 0.3 mm) for all layers
  • Pictures of current density and potential (by this voltage drop and resistance)
  • Pictures of temperature dependent conductivity and resistivity
  • Temperature at positions of virtual thermal couples
  • Heating curves or temperature response to power cycles.

What distinguishes TRM from PI-, SI- and CDF-software?

TRM is focusing on the low-frequency electro-thermal physics of a PCB and can be learned in one day of practice. Methods and algorithms are adapted to calculate mainly the complex PCBs easy and effective. High frequency effects (skin effect or induction) or fluid dynamics calculations are not performed.

How does TRM work?

TRM is primarily working with Gerber- and Excellon-Files, but also independently with pictures, colors, lists and some Microsoft standard software. TRM comes with a simple Gerber reader, your CAD system can export high resolution layout plots, or you are using ViewMate Pro by PentaLogix as an advanced and universal Gerber and drilling interface. If there is no layout available, create a sketch to scale in some 2D drawing software. To place components and pins on a plane, a build-in graphical editor is available. TRM is also open to communicate with your own software on request. After import the computational mesh is automatically created. The solution process can be monitored while calculating, the resulting gallery of pictures and report files are also created automatically.

How accurate is TRM?

In the end you would like to compare the results with a real thermography. Keep in mind that there are always tolerances, special manufacturing effects and influences of the measurement on the result itself. For a successful comparison, the computational and the experimental situation must match: no other sources of heat (humans, devices, lighting), no other sinks of heat (windows, sky, air conditioning) and no highly turbulent air movements (climate cabinets). At least power and current values must agree. Other typical sources of deviations are: copper thickness in input is not the final copper thickness after manufacturing; cables are influencing the temperature, either by addition or removal of heat; the electric resistance of a measurement wire is not small enough; a thermograph contains a weird mixture of emitted and reflected infrared radiation. If simulation model, device under duty and experimental setup are matching, the deviations of the simulations should be no larger than about +- 5%.

Trm multilayer accuracy

What does TRM not do?

TRM is not a layout or modeling tool. To model (preprocess) the board, please use your CAD layout software you and your colleagues are familiar with. You are exporting data, which are then interpreted by TRM, completed and compiled for a computable model. Your main focus is ease of use and effective calculation.

TRM is not an optimization tool. To get a better design, use the previous results and create a new design, routing or placement. However, materials, layer thickness, power and current values can be changed in TRM for a recalculation. TRM is not a 3D Finite-Element all-rounder. It is restricted to the electro-thermal aspects of the printed board and assembly. Enclosures and detailed component geometry can be brought in with some approximation only. As no air movement is calculated, CPU times are comparatively short.

Who should use TRM?

TRM has been designed to meet the demands of a 'normal' innovative electronics engineer or those of a consultant in an electronics manufacturing services (EMS) company. He can become independent from the calculation services department in big companies or he is able to bring in expertise into a small company without such specialists. Knowledge in numerical methods is not required. The modeler mainly is the company's layout tool. The TRM user interface brings the user to a result in seven steps. Special requests could be developed, implemented and licensed.

What are the benefits?

The calculated thermographs come in high-resolution. You can visualize hotspots and identify regions f thermo-mechanical stress, caused by high temperature differences on short distance. The calculated current density pictures show where there are bottlenecks, but also when constrictions create high current density but not much temperature excess because heat can flow into other parts of a trace. With little engineering experience, you can decide, whether a spot is real critical or not. This could not be achieved by any automated design rule check. When changing the layer thickness, number of layers or environment conditions, you can explore the thermal limits of the board. By proper combination of actions the outcome might be savings in raw material, machine drilling time or a better soldering result. The TRM software can simulate all types of multilayers, SMD components, embedded passives, pins, Inlays, busbars, adhesives, plugged and unplugged, blind and burried vias, as long as the PCB is more or less flat. Compare technologies yourself and test what is coolest and what is an economically reasonable compromise. Check out drilling time, costs of material, number of layers, foot print area and number of processing steps that are needed to achieve temperature compliance.

Simple Examples

1. Simple bilayer "MCP 1630" (by courtesy MicroChip GmbH, Munich). Supposed, there is one component with dominant power loss. What is the maximum power under following ambient conditions: air temperature =35 degC, PCB inside a plastic enclosure, maximum component temperature =100 degC ? Assign 100 degC to U4 and TRM responds with 0.22 Watts. The thermal resistance case to ambient would be (100 - 35) K /0.2 W = 300 K/W . Some other value would be reported, if other heat sources were on. Don't place other hot components inside the green coloured zone.


2. A 6 layer communication board. Test load on a TO chip and 2400 vias. A TO-220 is on top layer, a BGA is on bottom layer. Heat from TO cannot spread outside the BGA fanout.


3. Variations of the current-carrying capacity design rule IPC-2221. The IPC-2221 temperature-current curves can be reproduced with TRM by one trace on top and a full copper plane on bottom. However, if the local copper neighborhood of the trace is of other topology, other temperature values result for the same current. Here an example for a 1 oz layer, a 5 mm trace width and a current of 11 Amps. IPC-2221 gives a temperature rise of 20 K, with more or less copper we get a lower or a higher temperature.


What are typical fields of application of TRM?

The following table gives some overview of fields of applications and some options for optimization by electro-thermal simulation with TRM. Some points can be interchanged and mixed.

PCB assemblies Heating by components

Multilayers Minimum layer thickness Position of components Minimum distance between hot components Conduction Cooling via wedge locks (loss of cooling) Local cooling by vias 3D calculation of thermal resistances

LED boards Horizontal heat spreading

Vertical heat transport by vias and microvias Aluminium or ceramics substrates Heatsinks (approximate) and adhesives

Current carrying capacity of traces

Detailed voltage drop Electric resistance of design traces Background temperature level due to currents Thermal impedance Local heating effects at bottlenecks, thermal reliefs and vias Optimum copper thickness Inlays and busbars Multiple nets and power scenarios Maximum On-time in PWM cycle Short circuit currents

How TRM pays off?

A return of investment could be estimated by several considerations: Suppose a prototype is functional ok, but overheats in lab test. You have lost costs of board manufacturing, mounting and thermography. Avoid two faults and TRM pays off. Suppose the results of a simulation show, that temperature will be ok with lower copper thickness, then even a single simulation could pay off, if the lot size is large. Drilling of a single thermal via costs around 1 ct and too much drillings extend machine time. Use simulation to eliminate ineffective drills or find a better place. Verify yourself thermal proposals and suggestions of board manufacturers with your own board. Compare different technologies and chose what is best for your special design. Use the results to estimate costs.

Hardware and software requirements of TRM

Numerical simulation in engineering and science usually demand higher power for a PC. We recommend a 64- bit System. A good resolved multilayer would need between 2 and 6 Gigabyte RAM. Operating systems: Microsoft Windows: XP, Windows 7. 32-bit and 64-bit (preferred). The software is delivered either with a dongle license or a FlexNet license. Support and hotline will be maintained by ADAM Research.

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