階梯式均溫板之理論模型與參數分析

Abstract

本研究建立一擁有不同厚度之階梯式均溫板之理論模型，獲得階梯式均溫板於不同工作溫度下的最佳注水量與最大熱傳功率。對於毛細壓力，我們利用理論和Surface Evolver進行預測，並透過實驗進行驗證，比較使用20目與100目銅網所造成的差異。此外，我們對抽氣過程中的液體損失質量以及殘留的不可凝結氣體對最大熱傳功率的影響進行分析。 我們發現，使用Surface Evolver模擬液氣介面之曲率後，所計算得到之毛細壓力，與實驗之結果吻合，且Surface Evolver可考慮不同銅網結構內液面高度對毛細壓力之影響，避免理論毛細壓力會高估將近501%的問題。結果顯示，在階梯式均溫板的工作溫度為60°C時，使用20目銅網之均溫板，其最佳液體填充率為69.1%，最大熱傳功率可達41 W，而使用100目銅網之均溫板，其最佳液體填充率為79.8%，最大熱傳功率可達108 W。 在製程上，抽氣的目標壓力將影響均溫板內的不可凝結氣體殘留量，若不可凝結氣體較多，將使均溫板中的氣體流動壓降變大，降低最大熱傳功率，且不可凝結氣體在使用20目銅網時的影響較大，原因在於網目數越小時，蒸氣流動壓降占總壓降的比例較高，故不可凝結氣體的影響較大。在抽氣目標壓力為0.4 torr均溫板工作溫度為60°C時，殘留的不可凝結氣體將會讓使用20目及100目銅網之階梯式均溫板的最大熱傳功率分別下降21%及11%。若將抽氣目標壓力降低至0.08 torr，則不可凝結氣體對最大熱傳功率之影響可降低至13%及7%，且等溫抽氣過程會造成約3.5%的液體損失填充率。在製程上，若能透過二次除氣將目標壓力降至更低，即可將不可凝結氣體的影響降至更低，提高均溫板的最大熱傳功率。利用本研究所開發之理論預測模型，將能獲得均溫板製程上的重要參數，有助於提升均溫板的穩定性並降低產品的失效率。

To investigate the critical parameters of stepped vapor chamber, we develop a theoretical model to evaluate the best filling ratio and the maximal cooling rate at different working temperatures. In this model, capillary pressure is a key factor, which is calculated through Young-Laplace equation. We estimate the curvature of liquid-vapor interface required in the equation by theory, simulations using Surface Evolver, and experimental validation. The results show that the capillary pressure simulated by Surface Evolver agrees well with experiment, avoiding the overestimation of capillary pressure by theoretical prediction as much as 501%. At working temperature of 60°C, the stepped vapor chamber with the No.20 mesh screen achieves a maximal cooling rate of 41 W at a liquid filling ratio of 69.1%, while using the No.100 screen can reach 108 W at a liquid filling ratio of 79.8%. In addition, the effect of residual non-condensable gas (NCG) from the evacuation process is also considered. The results indicate that a lower target vacuum pressure helps to reduce the effect of NCG. when the target vacuum pressure is 0.08 torr, the residual NCG reduces the maximal cooling rate by 13% and 7% with the No. 20 and No. 100 mesh screens, respectively. With the isothermal assumption at 60°C, approximately 3.5% of the liquid filling ratio is lost during the evacuation for a target pressure of 0.08 torr. The theoretical model developed in this study provides critical insights that help to understand the internal mechanisms of stepped vapor chamber.