淺談多層電路板的阻抗知識
阻抗對於 多層電路板, 為什麼 多層電路板 需要阻抗? 本文首先介紹了什麼是阻抗及其類型, 然後介紹了原因 多層電路板 需要阻抗, and finally explains the meaning of impedance to PCB多層電路板. 跟隨編輯器瞭解更多資訊.
在有電阻的電路中, 電感, 和電容, 交流的障礙叫做阻抗. 阻抗通常用Z表示, 這是一個複數. 真正的部分叫做阻力, 虛部叫做電抗. 電路中電容對交流電的阻礙作用稱為電容電抗, 電路中電感對交流電的阻礙作用稱為電感電抗, 電路中電容和電感對交流電的阻礙作用統稱為電抗. 阻抗組織為歐姆.
(1) Characteristic impedance
In electronic information products such as computers and wireless communications, the energy transmitted by the circuit board in the circuit is a square wave signal (square wave signal, called pulse) composed of voltage and time, 它遇到的電阻叫做特性阻抗.
(2.) Odd Mode Impedance
The impedance value of one line to the ground of the two lines is the same as the impedance value of the two lines.
(3.) Even mode impedance
The two same signal waveforms with the same polarity are input to the drive terminal, 以及兩條導線連接在一起時的阻抗Zcom.
(4.) Differential impedance
Two identical signal waveforms with opposite polarities are input at the driving end, 分別由兩條差分線路傳輸, 兩個差分訊號在接收端相减. 差分阻抗是兩條導線之間的阻抗Zdiff.
(5) Common mode impedance
The impedance Zoe of one line to the ground of the two lines, 兩條線路的阻抗值相同, 通常大於奇數模阻抗.
多層電路板阻抗是指電阻和電抗的參數, 阻礙交流. 在生產過程中 PCB電路板, 阻抗處理至關重要. The reasons are as follows:
1. For multi-layer circuit boards (bottom of the board), 考慮插入和安裝電子元件. 封堵後, 考慮電導率和訊號傳輸效能等問題. 因此, 阻抗越低, 更好的, 電阻率應小於每平方釐米1.&TImes ; Below 10-6.
2. 多層電路板的生產過程必須經過沉銅過程, tin electroplating (or chemical plating, or thermal spray tin), 連接器焊接, 等., 而這些環節使用的資料必須保證電阻率低,以保證電路板的整體阻抗低,滿足產品品質要求,並能正常工作.
3. 鍍錫 多層電路板 是整個電路板生產中最容易出現的問題, 它是影響阻抗的關鍵環節. The biggest defect of the electroless tin coating is easy discoloration (easy to be oxidized or deliquescent) and poor solderability, 這將導致電路板焊接困難, 高阻抗, 導電性差, 或董事會整體績效不穩定.
4. 多層電路板的導體中將有各種訊號傳輸. 當必須新增頻率以提高其傳輸速率時, 由於蝕刻等因素,電路本身將導致阻抗值較高, 層壓板厚度, 和導線寬度. 這種變化導致訊號失真,電路板效能下降. 因此, 必須將阻抗值控制在一定範圍內.
電子行業, 根據行業調查, the most fatal weakness of the electroless tin coating is its easy discoloration (easy to be oxidized or deliquescent), 釺焊效能差導致焊接困難, 和高阻抗導致導電性差或整個電路板效能不穩定., 容易形成長錫須,導致PCB電路短路,甚至燒毀或起火.
據報導,20世紀90年代初,昆明理工大學在國內首次開展了化學鍍錫的研究, followed by Guangzhou Tongqian Chemical (enterprise) in the late 1990s. 到現在為止, 業界已經認識到這兩個機构是最好的. 其中, 根據我們的連絡人篩選調查, 許多公司的實驗觀察和長期耐久性測試, 經證實,通前化工的錫層為低電阻率的純錫層, 導電性和釺焊質量可保證在較高水準. 難怪他們敢於向外界保證塗層可以保持顏色一年, 無起泡, 無剝落, 和永久性錫須,無任何密封和防變色保護.
後來, 整個社會生產產業發展到一定程度, 許多後來的參與者經常相互複製. 事實上, a considerable number of companies themselves did not have the R&D or initiative capabilities themselves. 因此, many products and their usersâ electronic products (circuit boards) The bottom of the board or the overall electronic product) performance is poor, 而效能不佳的主要原因是阻抗問題, 因為在使用不合格的化學鍍錫工藝時, 電鍍在PCB多層電路板上. Tin is not really pure tin (or pure metal element), but a compound of tin (that is, 它根本不是金屬元素, 而是一種金屬化合物, 氧化物或鹵化物, 或者更直接, it is a non-metal substance) Or a mixture of tin compound and tin metal element, 但是用肉眼很難找到
因為多層電路板的主電路是銅箔, 銅箔的焊點是鍍錫的, and the electronic components are soldered on the tin-plated layer through solder paste (or solder wire). 事實上, 焊膏正在熔化. The molten state soldered between the electronic component and the tin plating layer is metal tin (that is, the metal element with good conductivity), 囙此可以簡單地指出,電子元件通過鍍錫層連接到電路板底部的銅箔上, 囙此,tin塗層的純度及其阻抗是關鍵; 但在電子元件插入之前, 當我們直接使用儀器檢測阻抗時, 事實上, the two ends of the instrument probe (or called the test lead) first touch the copper on the bottom of the PCB板. 然後將箔表面的鍍錫層連接到電路板底部的銅箔,以傳遞電流. 因此, 鍍錫是關鍵, 影響阻抗的鍵和影響整個電路板效能的鍵, 這也是容易被忽視的關鍵.
我們都知道, 除了簡單的金屬物質, its compounds are poor electrical conductors or even non-conductive (also, this is the key to the distribution capacity or spreading capacity in the circuit), 囙此,在錫化合物或混合物的情况下,鍍錫層中存在這種准導電性,而不是導電性, the existing resistivity or the resistivity after the electrolysis reaction due to future oxidation or damp and the corresponding impedance are quite high (enough to affect the level or signal transmission in the digital circuit) and The characteristic impedance is also not consistent. 囙此,它將影響電路板和整個機器的效能.
因此, 就當前的社會生產現象而言, 電路板底部的塗層材料和效能是影響整個電路板特性阻抗的最重要和最直接的原因. 因為它的可變性, 其阻抗的令人擔憂的影響變得更加不可見和多變. 其隱匿的主要原因有:一是, it cannot be seen by the naked eye (including its changes), 其次, 由於其隱蔽性,無法持續量測. 存在隨時間和環境濕度變化的可變性, 所以它總是很容易被忽視.