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Experimental Investigation of Temperature-Current Rise in Fine PCB Copper Traces on Polyimide , Aluminium and Ceramic ( Al 2 O 3 ) Substrates
| Content Provider | Semantic Scholar |
|---|---|
| Author | Petrosyants, Konstantin O. Popov, Anton A. |
| Copyright Year | 2013 |
| Abstract | Three types of copper traces for PCBs were investigated: 1) 2.5 μm thin film lines (Ti;Cu;Ni) on aluminium and ceramic (Al2O3) substrates; 2) 2.5 μm thin film lines (Ti;Cu;Ni;Au) on ceramic (Al2O3) substrates; 3) 15 μm traces (Cu;Ni) on polyimide substrate for high density interconnection PCBs. The width of all types of traces was varying in the range of 100-500 μm. The set of temperature-current diagrams for different PCB scenarios are presented and analyzed. The temperature caused by Joule heating was measured using IR camera Flir A40 with macrolens. For different cases the current was set in the range of 0.1-3 A; the measured temperature was in the range of 20-140 o C. The close agreement between the results measured and simulated with ELCUT software tool was achieved. Introduction The increasing demands for miniaturization and better functionality of electronic components and devices have a significant effect on the requirements facing the printed circuit board (PCB) industry. PCB manufactures are driving for producing high density interconnect (HDI) boards at significantly reduced cost and reduced implementation time. The interconnection complexity of the PCB is still growing and today calls for 50/50 μm or 25/25 μm technology are real. The wide requirements for higher power density in many power electronic applications, such as telecommunication and automobile, causes the current density in PCB traces increase constantly. How much current PCB traces are able to carry is a question that most of PCB designers concern about. Therefore, sizing PCB traces for a certain amount of temperature rise with applied currents is normally the first step of the PCB thermal management. The current carrying capacity (CCC) of PCB traces is the maximum current that can be applied in PCB traces to achieve maximum allowable temperature rises in traces. When current is applied to a conductor, its temperature rise is dependent upon its cross sectional area and factors such as the PB thickness, PB material, amount and adjacency of copper in the PB, and the environment in which PB is being operated. The mounting of the PB, environment (air, vacuum, forced air), copper plane layers, the components that the conductor is connected to, and length of the conductor are partial list of the things that can impact the conductor temperature rise. In previous works the problem of PCB CCC was investigated. In work [1] the traces with conductor thickness from 35 μm to 120 μm, width from 125 μm to 500 μm, board thickness from 0,78 mm to 1,6 mm were investigated. But the temperature rise was limited up to 50 o C. In standard IPC-2152 [2] the trace temperature rise exclusively depends on the conductor cross section area but the influence of varied trace length is neglected. Brooks [3] introduced separate dependence on trace width and thickness in his CCC equation by curve fitting techniques. Adam [4] expanded CCC charts of more board scenarios based on the verified mathematical model. In experimental work [5] the current carrying capability of FR-4 PCBs for high load currents was measured. In [6] the influence of a distance from trace edge to board edge and corner effect of FR-4 PCBs was investigated. In [7] the thermal coupling of parallel tracks of FR-4 PCBs was analyzed. Advanced Materials Research Vol. 739 (2013) pp 155-160 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.739.155 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 80.250.162.38-17/06/13,15:16:09) The results presented in mentioned above works are developed on PCBs with large sizes (thick base materials and large spacing between traces). Moreover, these results were received for traces with width more than 200 μm, thickness more than 18 μm and did not included CCC dependence on trace length. The traces on Al substrate and multi-layer traces (Ti;Cu;Ni) were not investigated. So they cannot reliably predict the trace CCC of modern PCBs. The purpose of this work is experimental CCC investigation for modern PCB traces taking into account the factors mentioned above. Traces on Polyimide Substrate This base material is used for flexible PCB production. In this work we investigate the CCC for fine traces of modern PCBs. In previous work [4] the CCC for traces with conventional sizes: substrate thickness 300 μm, trace width ≥ 200 μm, trace thickness 35 μm were investigated. In our work we investigated the CCC fine traces for HDI PCB technology. A board with several test structures was designed. The copper tracks with width (100 and 175 μm), and length (10, 30, 60, 120 mm) were studied. The base material is polyimide, board thickness is 24 μm, board sizes are 150x120 mm, trace thickness is 15 μm (12 μm Cu and 3 μm Ni). In Fig.1. the fragment of the trace with pad on polyimide substrate is presented. Ambient condition is “still air” (i.e. free convection) with Ta=20 o C. Two types of experiments were developed: 1) CCC dependence on track width (100 and 175 μm) and T-I characteristics for two parallel tracks with w=175 μm and 200 μm spacing, the length of all traces is 60 mm (Fig. 2). 2) CCC dependence on trace length l (10, 30, 60, 120 mm), trace width is w=100 μm (Fig. 3). Fig. 1. Fragment of the trace with pad on polyimide substrate. Fig. 2. Mean temperature of a trace as function Fig. 3. Mean temperature of a trace as function of electrical current for different trace widthes. of electrical current for different trace lengthes. It is seen in Fig. 2 that the critical temperature is growing with trace width decrease. The cross sections were obtained: 0.0012 mm2 and 0.0021 mm2. While the smallest cross section cannot carry more than 0.31 A, a two times larger cross section can carry up to approximately 0.5 A before reaching the same temperature. 0 20 40 60 80 100 120 140 0 0.1 0.2 0.3 0.4 0.5 T , o C I, A 2 parallel tracks |
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| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
