印刷线路板设计参数对镀通孔可靠性的影响

基于镀通孔(PTH, Plated Through-Hole)应力分布模型,定量地研究了PTH线路板厚度与PTH直径之比(高径比)、PTH半径与镀层厚度之比、线路板有效作用半径与PTH半径之比等几何设计参数以及线路板玻璃化温度对PTH镀层应变及寿命的影响.通过引入等效温度载荷,给出了不同玻璃化温度下的应力分布模型.研究表明,在屈服温度载荷附近时,PTH应变和寿命对几何尺寸非常敏感.在固定线路板有效作用半径与PTH半径之比后,PTH高径比影响较为明显.对于一定厚度的线路板,PTH半径越小,镀层最大应变越大,寿命越低.在玻璃化温度以上,应变急剧增加.研究还表明应变集中系数并非固定不变,而是在弹性和塑性范围内有所变化.

Effects of PWB design factors on PTH reliability

Based on the barrel stress distribution model,the effect of printed wiring board(PWB) design factors such as plated through-hole(PTH) aspect ratio,the ratio of plating thickness over PTH radius,the ratio of board influence radius over PTH radius and glass transition temperature on PTH barrel stress and lifetime were studied quantitatively.Equivalent temperature load was introduced to found the barrel stress distribution model under different glass transition temperature.Results show that PTH life is sensitive to design factors when PWB operating at vicinities of the yielding temperature load.The PTH aspect ratio shows more significant impact when fixing the ratio of board influence radius over PTH radius.For the fixed PWB thickness,decrease PTH diameter results in the increase of PTH barrel stress and the decrease of PTH lifetime.PTH barrel strain sharply increases at the glass transition temperature.Results also show that the constant strain concentration coefficient is different in elastic and plastic stage.