TWI771197B

TWI771197B - Welding structure of low temperature solder and its manufacturing method

Info

Publication number: TWI771197B
Application number: TW110136208A
Authority: TW
Inventors: 王彰盟
Original assignee: 昇貿科技股份有限公司
Priority date: 2021-09-29
Filing date: 2021-09-29
Publication date: 2022-07-11
Also published as: CN115884514A; TW202315474A

Abstract

本發明提供一種低溫焊錫的焊接結構，由下而上至少依序包含：一印刷電路板的一線路層、一介金屬化合物層、一第一焊接擴散層、一焊接金屬層、一第二焊接擴散層及一電子元件之一電極層。該印刷電路板的該線路層的表面處理是使用無鉛焊錫合金焊墊，使得焊接後的焊接結構擁有良好的冷熱循環信賴性。本發明還提供一種焊接結構的製造方法以製作前述低溫焊錫的焊接結構。The present invention provides a welding structure for low-temperature soldering, which comprises at least sequentially from bottom to top: a circuit layer of a printed circuit board, an intermetallic compound layer, a first welding diffusion layer, a welding metal layer, and a second welding diffusion layer layer and an electrode layer of an electronic component. The surface treatment of the circuit layer of the printed circuit board uses lead-free solder alloy pads, so that the soldered structure has good reliability of cold and heat cycles. The present invention also provides a manufacturing method of a welding structure to manufacture the aforementioned welding structure of low temperature solder.

Description

低溫焊錫的焊接結構及其製造方法Welding structure of low temperature solder and its manufacturing method

本發明是有關於一種電子元件的組裝焊接結構，特別是指一種利用低溫錫膏進行焊接而與電子元件形成的焊接結構，以形成高信賴性之低溫焊錫的焊接結構及其製造方法。The present invention relates to an assembly welding structure of electronic components, in particular to a welding structure formed with electronic components by welding with low temperature solder paste, so as to form a welding structure of high reliability low temperature solder and a manufacturing method thereof.

習知的組裝焊接過程上，印刷電路板(Printed circuit board，PCB)線路保護的表面處理多為塗佈有機保焊劑(Organic Solderability Preservative，OSP)層；電子元件的下表面則附著有錫或錫合金電極，例如晶片底部表面所附著的球柵陣列(ball grid array；簡稱BGA)。組裝的次序是將錫膏印刷於OSP層上之後，再將電子元件的電極置件於錫膏層上，再通過錫爐使錫膏熔融及擴散而形成焊接結構並完成組裝。In the conventional assembly and soldering process, the surface treatment of printed circuit board (Printed circuit board, PCB) circuit protection is mostly coated with an organic solder preservative (Organic Solderability Preservative, OSP) layer; the lower surface of electronic components is attached with tin or tin. Alloy electrodes, such as ball grid array (BGA) attached to the bottom surface of the wafer. The assembly sequence is after the solder paste is printed on the OSP layer, and then the electrodes of the electronic components are placed on the solder paste layer, and then the solder paste is melted and diffused through a tin furnace to form a solder structure and complete the assembly.

近來積體電路(integrated circuit，IC)晶片的高密度化使得其封裝結構多為薄而大面積。在利用SAC(錫銀銅)系錫膏焊接時因為焊接時的高溫約245℃~260℃會使IC的封裝結構在加熱過程中產生變形而失去平整度，導致空焊、短路等焊接的不良問題發生。因此降低焊接的溫度來減少IC封裝體的材料變形是改善焊接不良發生的方法之一。於是使用大量含鉍的低溫焊錫合金，例如鉍含量大於10%(重量百分比)的錫鉍合金錫膏(熔點約140℃~180℃)來降低焊接溫度成為解決的主要手法。With the recent high density of integrated circuit (IC) chips, most of the package structures thereof are thin and large. When using SAC (tin-silver-copper) solder paste for soldering, the high temperature during soldering is about 245 ° C ~ 260 ° C, which will cause the IC package structure to deform during the heating process and lose its flatness, resulting in empty soldering, short circuit and other welding defects. problem occurs. Therefore, reducing the soldering temperature to reduce the material deformation of the IC package is one of the methods to improve the occurrence of soldering defects. Therefore, using a large amount of bismuth-containing low-temperature solder alloys, such as tin-bismuth alloy solder paste with a bismuth content greater than 10% (weight percent) (melting point of about 140 ° C ~ 180 ° C), to reduce the welding temperature has become the main solution.

前述錫鉍合金錫膏因為熔點低在組裝時可低溫焊接以具有減少元件變形的優勢。使用一般OSP表面處理的PCB用錫鉍合金錫膏焊接時，因為電極多為純錫或錫銀銅等較高熔點的合金，所以為達成較好的焊接效果，前述錫鉍合金錫膏的溫度(熔點小於180℃)會比原來的熔點(熔點約140℃)增加約40℃以上或是增加較長迴焊的時間。此時錫鉍合金錫膏的流動性會變好，有時會造成大量的鉍擴散至例如BGA球的零件載板端形成金鉍的介金屬化合物(Inter-metallic Compound，IMC)，造成球與載板間的金脆問題；因此有限制鉍的擴散高度僅能達到BGA球的三分之一高度的要求。另外，以同樣的錫鉍合金錫膏在較低迴焊溫度時，雖然不會使鉍大量往上擴散，會造成銅線路上部大區域的錫鉍集中區。這樣會使得焊接部(稱為錫鉍焊接層)形成一個只有低溫焊接層及高脆性的區域。這區域一旦形成會使得焊接部位除了不耐機械衝擊(例如摔落測試)之外，最容易造成的問題是在冷熱循環下重複的高低溫環境中鉍容易產生擴散，造成富鉍相的成長而形成空孔，再加上熱脹冷縮的應力作用下，會使得錫鉍區發生斷裂問題，也就是所謂的熱撕裂現象(hot-tearing)，因而造成低溫焊錫焊接部的信賴性不如傳統的錫銀銅合金SAC305焊錫形成的焊接層。雖然含鉍之銲錫合金種類很多，在與OSP表面處理焊接時，卻很難避免這個現象發生。The aforementioned tin-bismuth alloy solder paste can be soldered at low temperature during assembly due to its low melting point, which has the advantage of reducing component deformation. When using tin-bismuth alloy solder paste to solder PCBs with general OSP surface treatment, because the electrodes are mostly pure tin or tin-silver-copper alloys with higher melting points, in order to achieve a better welding effect, the temperature of the aforementioned tin-bismuth alloy solder paste (melting point less than 180°C) will increase by about 40°C or more than the original melting point (melting point is about 140°C) or increase the reflow time for a longer time. At this time, the fluidity of the tin-bismuth alloy solder paste will become better, and sometimes a large amount of bismuth will diffuse to the part carrier end of the BGA ball to form an inter-metallic compound (IMC) of gold and bismuth, causing the ball to interact with The problem of gold brittleness between the carriers; therefore, there is a requirement to limit the diffusion height of bismuth to only one-third of the height of the BGA ball. In addition, when the same tin-bismuth alloy solder paste is used at a lower reflow temperature, although a large amount of bismuth will not diffuse upward, it will cause a large area of tin-bismuth concentration in the upper part of the copper circuit. This results in a solder joint (called a tin-bismuth solder layer) forming a region with only a low-temperature solder layer and high brittleness. Once this area is formed, in addition to mechanical shock resistance (such as drop test), the most likely problem is that bismuth is easily diffused in repeated high and low temperature environments under cold and heat cycles, resulting in the growth of bismuth-rich phases. The formation of voids, coupled with the stress of thermal expansion and contraction, will cause the tin-bismuth zone to fracture, which is the so-called hot-tearing phenomenon, resulting in low-temperature soldering The reliability of the solder joint is not as good as the traditional one. The solder layer formed by the tin-silver-copper alloy SAC305 solder. Although there are many types of bismuth-containing solder alloys, it is difficult to avoid this phenomenon when soldering with OSP surface treatment.

因此，本發明之目的，即在提供一種低溫焊錫的焊接結構，該低溫焊錫的焊接結構是使用無鉛焊錫合金焊墊的印刷電路板，這使得結合電子元件後的焊接結構擁有良好的耐冷熱循環信賴性。Therefore, the purpose of the present invention is to provide a welding structure of low temperature solder, the welding structure of the low temperature solder is a printed circuit board using lead-free solder alloy pads, which makes the welding structure combined with electronic components have good resistance to cold and heat cycles Reliability.

基於上述發明目的，提供一種低溫焊錫的焊接結構，至少包含：一線路層；一介金屬化合物(Inter-metallic Compound，IMC)層，該IMC層形成於該線路層的上面；一第一焊接擴散層，該第一焊接擴散層形成於該IMC層的上面；一焊接金屬層，該焊接金屬層形成於該第一焊接擴散層的上部；一第二焊接擴散層，該第二焊接擴散層形成於該焊接金屬層的上部；一電子元件之一電極層，該電極層位於該第二焊接擴散層的上部。Based on the above purpose of the invention, a welding structure of low temperature solder is provided, which at least comprises: a circuit layer; an Inter-metallic Compound (IMC) layer, the IMC layer is formed on the circuit layer; a first welding diffusion layer , the first welding diffusion layer is formed on the top of the IMC layer; a welding metal layer is formed on the upper part of the first welding diffusion layer; a second welding diffusion layer is formed on the The upper part of the welding metal layer; an electrode layer of an electronic component, the electrode layer is located on the upper part of the second welding diffusion layer.

依據上述低溫焊錫的焊接結構，該線路層是一含銅的銅線路，該IMC層主要為銅與錫反應形成的金屬化合物，是於低溫焊接時為一焊墊結構製作時所形成。該第一焊接擴散層為一無鉛焊錫合金焊墊層於焊接時因為一無鉛錫鉍合金錫膏中鉍的擴散進入後而形成的下鉍擴散層。該焊接金屬層為一無鉛錫鉍合金層，為該無鉛錫鉍合金錫膏在焊接後其中的鉍未擴散之部分。該第二焊接擴散層為於焊接時該無鉛錫鉍合金錫膏中的鉍擴散進入該電極層所造成的上鉍擴散層。該電極層是一含錫或錫合金電極層，或是附著於一電子元件的下表面或封裝結構下輸入/輸出(I/O)的錫合金球(例如BGA球)。According to the above-mentioned low-temperature soldering structure, the circuit layer is a copper-containing copper circuit, and the IMC layer is mainly a metal compound formed by the reaction of copper and tin, which is formed when a pad structure is fabricated during low-temperature soldering. The first solder diffusion layer is a lower bismuth diffusion layer formed by a lead-free solder alloy pad layer due to diffusion of bismuth in a lead-free tin-bismuth alloy solder paste during soldering. The soldering metal layer is a lead-free tin-bismuth alloy layer, which is a part of the lead-free tin-bismuth alloy solder paste in which the bismuth is not diffused after soldering. The second solder diffusion layer is an upper bismuth diffusion layer caused by the diffusion of bismuth in the lead-free tin-bismuth alloy solder paste into the electrode layer during soldering. The electrode layer is a tin-containing or tin alloy electrode layer, or tin alloy balls (eg BGA balls) attached to the lower surface of an electronic component or input/output (I/O) under the package structure.

本發明基於前述低溫焊錫的焊接結構，又提供一種焊接結構的製造方法，係依序包含以下步驟：一提供有無鉛焊錫合金焊墊的印刷電路板步驟、一印刷低溫錫鉍合金錫膏步驟、一置件電子元件步驟及一迴焊加熱步驟。The present invention is based on the welding structure of the aforementioned low-temperature solder, and further provides a manufacturing method of the welding structure, which includes the following steps in sequence: a step of providing a printed circuit board with lead-free solder alloy pads, a step of printing a low-temperature tin-bismuth alloy solder paste, A step of placing electronic components and a step of reflow heating.

首先請參閱第1圖，本發明之一種焊墊結構1由下而上至少依序包含：一印刷電路板10、一線路層11、一IMC層12及一無鉛焊錫合金焊墊層A。該線路層11位於該印刷電路板10的上表面且通常是一導電線路圖案，該線路層11的材料可以是銅，換言之該線路層11是銅線路。該IMC層12形成於該線路層11的上表面，該IMC層12主要為銅與錫或其他元素形成的金屬化合物。該無鉛焊錫合金焊墊層A位於該IMC層12的上表面，該無鉛焊錫合金焊墊層A的材料包含錫，例如為含錫合金，較佳為錫銀銅合金或錫銅合金或其他含1wt%以下的鉍的無鉛焊錫合金。於實際運用時可以是無鉛焊料SAC305 (Sn 96.5wt%、Ag 3.0wt%、Cu 0.5wt%)或SAC0307(Sn 99.0wt%、Ag 0.3wt%、Cu 0.7wt%)。較佳地，該無鉛焊錫合金焊墊層A的材料不含故意添加的鉍。又或者，該無鉛焊錫合金焊墊層A為一含錫合金層或含小於1wt%鉍的無鉛焊錫合金層。這種無鉛焊錫合金層(該無鉛焊錫合金焊墊層A)可以使用電鍍、噴錫或是錫膏加熱法及其他方法來形成，厚度約10μm ~100μm(微米)，但不包含高濃度鉍(大於1wt%)的合金。需先說明的是，本發明所指的「無鉛」是實質是符合RoHS(Restriction of Hazardous Substances，關於限制在電子電器設備中使用某些有害成分的指令)的無鉛規範定義。前述實質上不包含鉛是指原則上只要非蓄意在合金中添加鉛(例如於製造過程中無意但不可避免的雜質或接觸)，因此即可被視為實質上不包含鉛或可視為無鉛。「wt%」指的是重量百分比，另外，本發明所述之數值範圍的限定總是包括端值。First, please refer to FIG. 1 , a pad structure 1 of the present invention includes at least sequentially from bottom to top: a printed circuit board 10 , a circuit layer 11 , an IMC layer 12 and a lead-free solder alloy pad layer A. The circuit layer 11 is located on the upper surface of the printed circuit board 10 and is usually a conductive circuit pattern. The circuit layer 11 may be made of copper, in other words, the circuit layer 11 is a copper circuit. The IMC layer 12 is formed on the upper surface of the circuit layer 11 , and the IMC layer 12 is mainly a metal compound formed by copper and tin or other elements. The lead-free solder alloy pad layer A is located on the upper surface of the IMC layer 12 , and the material of the lead-free solder alloy pad layer A includes tin, such as a tin-containing alloy, preferably a tin-silver-copper alloy or a tin-copper alloy or other alloys containing tin. Lead-free solder alloys containing less than 1wt% bismuth. In practice, it can be lead-free solder SAC305 (Sn 96.5wt%, Ag 3.0wt%, Cu 0.5wt%) or SAC0307 (Sn 99.0wt%, Ag 0.3wt%, Cu 0.7wt%). Preferably, the material of the lead-free solder alloy pad layer A does not contain intentionally added bismuth. Alternatively, the lead-free solder alloy pad layer A is a tin-containing alloy layer or a lead-free solder alloy layer containing less than 1 wt % bismuth. The lead-free solder alloy layer (the lead-free solder alloy pad layer A) can be formed by electroplating, tin spraying or solder paste heating and other methods, and has a thickness of about 10 μm to 100 μm (microns), but does not contain high concentrations of bismuth ( greater than 1 wt%). It should be noted that the "lead-free" referred to in the present invention is essentially a lead-free standard definition that complies with RoHS (Restriction of Hazardous Substances, the directive on restricting the use of certain harmful components in electrical and electronic equipment). The aforementioned substantially free of lead means that in principle, as long as lead is not intentionally added to the alloy (eg, unintentional but unavoidable impurities or contact during the manufacturing process), it can be regarded as substantially free of lead or can be regarded as lead-free. "wt %" refers to weight percent, and further, definitions of numerical ranges stated herein are always inclusive.

請參閱第2圖，本發明之一種低溫焊錫的焊接結構100由下往上依序包含該線路層11、該IMC層12、一第一焊接擴散層13、一焊接金屬層14、一第二焊接擴散層15、一電子元件17的一電極層16。其中，該IMC層12形成於該線路層11的上面；該第一焊接擴散層13形成於該IMC層12的上面；該焊接金屬層14形成於該第一焊接擴散層13的上部；該第二焊接擴散層15形成於該焊接金屬層14的上部；該電極層16位於該第二焊接擴散層15的上部，該電極層16也是附著於該電子元件17的下表面。Please refer to FIG. 2 , a low-temperature solder soldering structure 100 of the present invention sequentially includes the circuit layer 11 , the IMC layer 12 , a first solder diffusion layer 13 , a solder metal layer 14 , and a second solder layer from bottom to top. Solder the diffusion layer 15 and an electrode layer 16 of an electronic component 17 . Wherein, the IMC layer 12 is formed on the top of the circuit layer 11; the first solder diffusion layer 13 is formed on the top of the IMC layer 12; the solder metal layer 14 is formed on the upper part of the first solder diffusion layer 13; Two solder diffusion layers 15 are formed on the upper part of the solder metal layer 14 ; the electrode layer 16 is located on the upper part of the second solder diffusion layer 15 , and the electrode layer 16 is also attached to the lower surface of the electronic element 17 .

該第一焊接擴散層13為一含有錫及鉍的下鉍擴散層，該焊接金屬層14為一含有錫及鉍的錫鉍合金層，該第二焊接擴散層15為一含有錫及鉍的上鉍擴散層，該電極層16是一含錫的焊錫合金電極層。The first welding diffusion layer 13 is a lower bismuth diffusion layer containing tin and bismuth, the welding metal layer 14 is a tin-bismuth alloy layer containing tin and bismuth, and the second welding diffusion layer 15 is a On the bismuth diffusion layer, the electrode layer 16 is a tin-containing solder alloy electrode layer.

該低溫焊錫的焊接結構100是以一焊接結構的製造方法所製作，該焊接結構的製造方法依序包含以下步驟。The welding structure 100 of the low temperature solder is fabricated by a manufacturing method of a welding structure, and the manufacturing method of the welding structure includes the following steps in sequence.

一提供有無鉛焊錫合金焊墊的印刷電路板步驟：提供該焊墊結構1，焊墊結構1由下而上至少依序包含：該印刷電路板10、該線路層11、該IMC層12及該無鉛焊錫合金焊墊層A。A step of providing a printed circuit board with lead-free solder alloy pads: providing the pad structure 1, the pad structure 1 at least sequentially includes: the printed circuit board 10, the circuit layer 11, the IMC layer 12 and the The lead-free solder alloy pad layer A.

一印刷低溫錫鉍合金錫膏步驟：將該焊墊結構1以一含鉍的低溫錫膏(無鉛錫鉍合金錫膏)印刷於該焊墊結構1的該無鉛焊錫合金焊墊層A的上表面，例如該無鉛錫鉍合金錫膏係為錫鉍錫膏(例如42wt%的錫及58wt%的鉍)，或者錫鉍銀錫膏(例如42wt%的錫、57wt%的鉍及1wt%的銀)。或者，以錫鉍為主成分添加數ppm至數wt%的其他一種或一種以上之金屬元素之低溫錫膏。A step of printing low-temperature tin-bismuth alloy solder paste: the solder pad structure 1 is printed on the lead-free solder alloy solder pad layer A of the solder pad structure 1 with a low-temperature solder paste containing bismuth (lead-free tin-bismuth alloy solder paste) For example, the lead-free tin-bismuth alloy solder paste is a tin-bismuth solder paste (such as 42wt% tin and 58wt% bismuth), or a tin-bismuth-silver paste (such as 42wt% tin, 57wt% bismuth and 1wt% bismuth) silver). Alternatively, a low-temperature solder paste containing tin and bismuth as the main component and adding several ppm to several wt% of other one or more metal elements.

一置件電子元件步驟：將該電子元件17的該電極層16疊置於該無鉛錫鉍合金錫膏的上面，也就是說中間製程是該電子元件17或BGA球疊置於該無鉛錫鉍合金錫膏的上面以形成一焊接結構半成品。A step of placing electronic components: the electrode layer 16 of the electronic component 17 is stacked on the top of the lead-free tin-bismuth alloy solder paste, that is to say, the electronic component 17 or the BGA ball is stacked on the lead-free tin-bismuth in the intermediate process. Alloy solder paste on top to form a semi-finished solder structure.

一迴焊加熱步驟：將該焊接結構半成品以160℃~190℃進行加熱4.5分鐘~6.5分鐘(例如以迴焊爐加熱)，接著冷卻例如冷卻至室溫25℃。於本迴焊加熱步驟過程中，該無鉛錫鉍合金錫膏中的鉍會部分往下遷移(也可稱為擴散)至該無鉛焊錫合金焊墊層A而使該無鉛焊錫合金焊墊層A變成該第一焊接擴散層13，換言之該第一焊接擴散層13為該無鉛焊錫合金焊墊層A於加熱時因為該無鉛錫鉍合金錫膏中鉍的擴散而形成的下鉍擴散層；該無鉛錫鉍合金錫膏中的鉍也會部分往上遷移至該電極層16的下部而使該電極層16的下部變成該第二焊接擴散層15，換言之該第二焊接擴散層15為於加熱時該無鉛錫鉍合金錫膏中的鉍擴散進入該電極層16的下部所造成的上鉍擴散層；該無鉛錫鉍合金錫膏則於加熱時形成該焊接金屬層14，該焊接金屬層14為一錫鉍合金層，為該無鉛錫鉍合金錫膏在焊接後其中的鉍未擴散之部分。據以，獲得該低溫焊錫的焊接結構100。其中，該第一焊接擴散層13中鉍的濃度小於該焊接金屬層14中鉍的濃度，該第二焊接擴散層15中鉍的濃度小於該焊接金屬層14中鉍的濃度。One reflow heating step: the semi-finished welded structure is heated at 160°C to 190°C for 4.5 minutes to 6.5 minutes (eg, heated in a reflow oven), and then cooled, eg, to a room temperature of 25°C. During this reflow heating step, part of the bismuth in the lead-free tin-bismuth alloy solder paste will migrate down (also referred to as diffusion) to the lead-free solder alloy pad layer A to make the lead-free solder alloy pad layer A It becomes the first solder diffusion layer 13, in other words, the first solder diffusion layer 13 is the lower bismuth diffusion layer formed by the diffusion of bismuth in the lead-free tin-bismuth alloy solder paste when the lead-free solder alloy pad layer A is heated; the Part of the bismuth in the lead-free tin-bismuth alloy solder paste will also migrate up to the lower part of the electrode layer 16 so that the lower part of the electrode layer 16 becomes the second solder diffusion layer 15 . In other words, the second solder diffusion layer 15 is used for heating When the bismuth in the lead-free tin-bismuth alloy tin paste diffuses into the upper bismuth diffusion layer caused by the lower part of the electrode layer 16; the lead-free tin-bismuth alloy tin paste forms the welding metal layer 14 when heated, and the welding metal layer 14 It is a tin-bismuth alloy layer, which is the undiffused part of bismuth in the lead-free tin-bismuth alloy solder paste after soldering. Accordingly, the welding structure 100 of the low-temperature solder is obtained. The concentration of bismuth in the first welding diffusion layer 13 is lower than the concentration of bismuth in the welding metal layer 14 , and the concentration of bismuth in the second welding diffusion layer 15 is lower than the concentration of bismuth in the welding metal layer 14 .

如果不使用該無鉛焊錫合金焊墊層，則於製作低溫焊錫的焊接結構時無法形成該下鉍擴散層(即該第一焊接擴散層)，換言之就如同先前技術所言的使用一般OSP表面處理的PCB用錫鉍合金錫膏焊接時，只會形成焊接金屬層上面的鉍擴散層(上鉍擴散層)而不會有下面的鉍擴散層(下擴散層)形成。然而本發明這樣的組織結構及方法相對先前技術來說可以有以下的優點：(1)減少錫鉍合金層(即該焊接金屬層14)厚度，避免硬脆及低溫區域過大；(2)可以同時形成上、下擴散層且上、下擴散層的鉍含量比該焊接金屬層14少，所以韌性比先前技術的錫鉍焊接層大且熔點也較高，可避免熱撕裂(Hot tearing)效應及脆性高；(3)在該迴焊加熱步驟的過程中，由於該無鉛錫鉍合金錫膏並不會與該線路層11的銅接觸，因此該無鉛錫鉍合金錫膏中的鉍不會受到鉍與銅相容性不佳所導致的熱力學效應而使得大量的鉍單方面往電極層端擴散至例如BGA球的零件端的問題，因此本發明很容易達到第二焊接擴散層的高度低於三分之一的BGA球的高度之要求。因此相較於先前技術而言，本發明該低溫焊錫焊接結構100有較佳的冷熱循環信賴性，其相關實施例證將於後述舉例。If the lead-free solder alloy pad layer is not used, the lower bismuth diffusion layer (ie, the first solder diffusion layer) cannot be formed during the fabrication of the low-temperature solder solder structure, in other words, the general OSP surface treatment is used as in the prior art When the PCB is soldered with tin-bismuth alloy solder paste, only the bismuth diffusion layer (upper bismuth diffusion layer) above the welding metal layer is formed without the formation of the lower bismuth diffusion layer (lower diffusion layer). However, the structure and method of the present invention can have the following advantages over the prior art: (1) reduce the thickness of the tin-bismuth alloy layer (that is, the welding metal layer 14 ) to avoid hard brittleness and excessive low temperature regions; (2) can The upper and lower diffusion layers are formed at the same time, and the bismuth content of the upper and lower diffusion layers is less than that of the welding metal layer 14, so the toughness is higher than that of the tin-bismuth welding layer of the prior art and the melting point is higher, which can avoid hot tearing (Hot tearing) (3) During the reflow heating step, since the lead-free tin-bismuth alloy solder paste does not contact the copper of the circuit layer 11, the bismuth in the lead-free tin-bismuth alloy solder paste is not Due to the thermodynamic effect caused by the poor compatibility of bismuth and copper, a large amount of bismuth unilaterally diffuses to the end of the electrode layer to the end of the part such as the BGA ball. Therefore, the present invention can easily achieve a low height of the second welding diffusion layer. less than one-third the height of a BGA ball. Therefore, compared with the prior art, the low-temperature soldering structure 100 of the present invention has better reliability in cooling and heating cycles, and relevant embodiments thereof will be described later.

＜實施例1~3與比較例1~3＞<Examples 1 to 3 and Comparative Examples 1 to 3>

實施例1~3與比較例1~3是使用有25顆*25顆陣列錫球的BGA球(即為前述電極層16，SAC305成分為96.5wt%的錫、3.0wt%的銀及0.5wt%的銅，球徑為0.45mm)的電子元件。表1中所對應的含鉍的錫膏是以鋼板印刷方式進行印刷。實施例1~3的PCB上的焊墊為約25μm的無鉛焊錫合金焊墊層，而含鉍的錫膏的印刷厚度為50μm，迴焊的峰值約190℃。比較例1~3的PCB上的焊墊為OSP，而含鉍的錫膏的印刷厚度為100μm，以跟實施例同樣的迴焊曲線進行焊接。其中，比較例1~3的焊墊結構(OSP焊墊)由下而上依序由印刷電路板、線路及OSP層所構成，此為一般所習知故不在此贅述；而實施例1~3的焊墊結構(無鉛焊錫合金焊墊)由下而上依序是由該印刷電路板10、該線路層11、該IMC層12及無鉛焊錫合金焊墊層A所構成，此為本發明的結構。接著再分別將比較例1~3與實施例1~3的焊接結構放入冷熱循環測試機，進行冷熱循環的信賴性測試。在冷熱循環測試機的測試是以低溫-40℃保持7分鐘後，再以升溫速度為15℃/min的方式直到達高溫100℃並於100℃保持7分鐘後，接著再以降溫速度為15℃/min的方式直到-40℃，以這樣視為一個循環(cycle)。以第500個循環、第1000個循環及第2000個循環將焊接結構取出，對取出之後的焊接結構中的堆疊架構進行裂痕觀察及量測。判斷標準是：裂痕的長度大於25μm以上時判斷為不良發生，為熱撕裂(hot-tearing)發生的證據，在第500個循環、第1000個循環及第2000個循環中的出現不良數目作為實施例與比較例的對比。Examples 1-3 and Comparative Examples 1-3 use BGA balls with 25*25 array tin balls (that is, the aforementioned electrode layer 16, and the SAC305 composition is 96.5wt% tin, 3.0wt% silver and 0.5wt%). % copper, electronic components with a ball diameter of 0.45mm). The corresponding bismuth-containing solder pastes in Table 1 were printed by stencil printing. The solder pads on the PCBs of Examples 1 to 3 are lead-free solder alloy solder pad layers of about 25 μm, while the printing thickness of the bismuth-containing solder paste is 50 μm, and the peak value of reflow is about 190°C. The pads on the PCBs of Comparative Examples 1 to 3 were OSP, and the printing thickness of the bismuth-containing solder paste was 100 μm, and the soldering was carried out with the same reflow curve as the Example. Wherein, the pad structures (OSP pads) of Comparative Examples 1 to 3 are composed of printed circuit boards, circuits and OSP layers in sequence from bottom to top, which are generally known and will not be repeated here; 3. The pad structure (lead-free solder alloy pad) is sequentially composed of the printed circuit board 10, the circuit layer 11, the IMC layer 12 and the lead-free solder alloy pad layer A from bottom to top, which is the present invention Structure. Then, the welded structures of Comparative Examples 1 to 3 and Examples 1 to 3 were put into a cold-heat cycle tester, respectively, to conduct a reliability test of the cold-heat cycle. In the test of the cold and heat cycle tester, after keeping the low temperature at -40°C for 7 minutes, the heating rate is 15°C/min until it reaches a high temperature of 100°C, and then the temperature is kept at 100°C for 7 minutes, and then the cooling rate is 15°C/min. °C/min up to -40 °C, which is regarded as a cycle. The welded structure was taken out at the 500th cycle, the 1000th cycle and the 2000th cycle, and crack observation and measurement were performed on the stacked structure in the welded structure after taking out. Judgment criteria are: when the length of the crack is more than 25 μm or more, it is judged that the defect has occurred, which is the evidence of hot-tearing, and the number of defects in the 500th cycle, the 1000th cycle and the 2000th cycle is regarded as the occurrence of the defect. Comparison of Examples and Comparative Examples.

表1 實施例1 比較例1 實施例2 比較例2 實施例3 比較例3 無鉛焊錫合金焊墊或OSP焊墊 SAC305 OSP SAC305 OSP SAC0307 OSP 含鉍的錫膏 SnBi SnBi SnBiAg SnBiAg SnBi SnBi 500次循環後的不良數目 0 2 0 1 0 2 1000次循環後的不良數目 0 10 0 8 1 12 2000次循環後的不良數目 1 16 0 12 2 17 SAC305：96.5wt%的錫、3.0wt%的銀、0.5wt%的銅； SAC0307：99.0wt%的錫、0.3wt%的銀、0.7wt%的銅； SnBi：42wt%的錫及58wt%的鉍； SnBiAg：42wt%的錫、57wt%的鉍及1wt%的銀。 Table 1 Example 1 Comparative Example 1 Example 2 Comparative Example 2 Example 3 Comparative Example 3 Lead-free solder alloy pads or OSP pads SAC305 OSP SAC305 OSP SAC0307 OSP Bismuth-containing solder paste SnBi SnBi SnBiAg SnBiAg SnBi SnBi Bad number after 500 cycles 0 2 0 1 0 2 Bad number after 1000 cycles 0 10 0 8 1 12 Bad number after 2000 cycles 1 16 0 12 2 17 SAC305: 96.5wt% tin, 3.0wt% silver, 0.5wt% copper; SAC0307: 99.0wt% tin, 0.3wt% silver, 0.7wt% copper; SnBi: 42wt% tin and 58wt% Bismuth; SnBiAg: 42wt% tin, 57wt% bismuth and 1wt% silver.

由表1，實施例1的最大不良數目為1個，比較例1的最大不良數目為16個，實施例1的不良發生(即發生熱撕裂hot tearing)的量遠小於比較例1，顯然地本發明的實施例1的焊接結構改善了比較例1的傳統焊接結構在冷熱循環的信賴性。實施例3的最大不良數目為2個，比較例3的最大不良數目為17個，實施3的不良發生的量遠小於比較例3，顯然地本發明的實施例3的焊接結構改善了比較例3的傳統焊接結構在冷熱循環的信賴性。實施例2的最大不良數目為0個，比較例2的最大不良數目為12個，實施例2的不良發生的量遠小於比較例2，顯然地本發明的實施例2的焊接結構改善了比較例2的傳統焊接結構在冷熱循環的信賴性。From Table 1, the maximum number of defects in Example 1 is 1, and the maximum number of defects in Comparative Example 1 is 16. The amount of defects (that is, hot tearing) in Example 1 is much smaller than that in Comparative Example 1. Obviously, Therefore, the welding structure of Example 1 of the present invention improves the reliability of the conventional welding structure of Comparative Example 1 in cooling and heating cycles. The maximum number of defects in Example 3 is 2, and the maximum number of defects in Comparative Example 3 is 17. The number of defects in Example 3 is much smaller than that in Comparative Example 3. Obviously, the welding structure of Example 3 of the present invention improves the comparative example. 3. The reliability of the traditional welded structure in the cooling and heating cycle. The maximum number of defects in Example 2 is 0, and the maximum number of defects in Comparative Example 2 is 12. The amount of defects in Example 2 is much smaller than that in Comparative Example 2. Obviously, the welding structure of Example 2 of the present invention improves the comparison. The reliability of the conventional welded structure of Example 2 in the cooling and heating cycle.

綜上所述，本發明的低溫焊錫的焊接結構與傳統結構相比較下，本發明具有優良的冷熱循環的信賴性，故確實能達成本發明之目的。To sum up, compared with the traditional structure, the welding structure of the low-temperature solder of the present invention has excellent reliability of the cooling and heating cycle, so it can indeed achieve the purpose of the present invention.

惟以上所述者，僅為本發明之實施例而已，當不能以此限定本發明實施之範圍，凡是依本發明申請專利範圍及專利說明書內容所作之簡單的等效變化與修飾，皆仍屬本發明專利涵蓋之範圍內。However, the above are only examples of the present invention, and should not limit the scope of the present invention. All simple equivalent changes and modifications made according to the scope of the application for patent of the present invention and the contents of the patent specification are still within the scope of the present invention. within the scope of the invention patent.

1:焊墊結構 10:印刷電路板 11:線路層 12:IMC層 13:第一焊接擴散層 14:焊接金屬層 15:第二焊接擴散層 16:電極層 17:電子元件 100:焊接結構 A:無鉛焊錫合金焊墊層1: Pad structure 10: Printed Circuit Board 11: Circuit layer 12: IMC layer 13: The first solder diffusion layer 14: Solder the metal layer 15: Second Solder Diffusion Layer 16: Electrode layer 17: Electronic Components 100: Welded structure A: Lead-free solder alloy pad layer

本發明之其他的特徵及功效，將於參照圖式的實施方式中清楚地呈現，其中：第1圖是本發明焊墊結構的結構示意圖。第2圖是本發明焊接結構的結構示意圖。 Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, wherein: FIG. 1 is a schematic structural diagram of the pad structure of the present invention. Fig. 2 is a schematic structural diagram of the welding structure of the present invention.

10:印刷電路板 10: Printed Circuit Board

11:線路層 11: Circuit layer

12:IMC層 12: IMC layer

13:第一焊接擴散層 13: The first solder diffusion layer

14:焊接金屬層 14: Solder the metal layer

15:第二焊接擴散層 15: Second Solder Diffusion Layer

16:電極層 16: Electrode layer

17:電子元件 17: Electronic Components

100:焊接結構 100: Welded structure

Claims

一種低溫焊錫的焊接結構，至少包含：一線路層(11)；一介金屬化合物(Inter-metallic Compound，IMC)層(12)，該IMC層(12)形成於該線路層(11)的上面；一第一焊接擴散層(13)，該第一焊接擴散層(13)形成於該IMC層(12)的上面；一焊接金屬層(14)，該焊接金屬層(14)形成於該第一焊接擴散層(13)的上部；一第二焊接擴散層(15)，該第二焊接擴散層(15)形成於該焊接金屬層(14)的上部；以及一電極層(16)，該電極層(16)位於該第二焊接擴散層(15)的上部。 A welding structure of low-temperature solder, comprising at least: a circuit layer (11); an Inter-metallic Compound (IMC) layer (12), the IMC layer (12) is formed on the circuit layer (11); a first solder diffusion layer (13), the first solder diffusion layer (13) is formed on the IMC layer (12); a welding metal layer (14), the welding metal layer (14) is formed on the upper part of the first welding diffusion layer (13); a second solder diffusion layer (15) formed on the upper portion of the solder metal layer (14); and an electrode layer (16), the electrode layer (16) is located on the upper part of the second solder diffusion layer (15).

如請求項1所述的低溫焊錫的焊接結構，其中，該線路層(11)是一含銅的銅線路。The welding structure of low-temperature solder according to claim 1, wherein the circuit layer (11) is a copper circuit containing copper.

如請求項2所述的低溫焊錫的焊接結構，其中，該IMC層(12)為銅與錫的金屬化合物。The soldering structure of low-temperature solder according to claim 2, wherein the IMC layer (12) is a metal compound of copper and tin.

如請求項3所述的低溫焊錫的焊接結構，其中，該第一焊接擴散層(13)為一含有錫及鉍的下鉍擴散層。The welding structure of low-temperature solder according to claim 3, wherein the first welding diffusion layer (13) is a lower bismuth diffusion layer containing tin and bismuth.

如請求項4所述的低溫焊錫的焊接結構，其中，該焊接金屬層(14)為一含有錫及鉍的錫鉍合金層，該第二焊接擴散層(15)為一含有錫及鉍的上鉍擴散層，該第一焊接擴散層(13)中鉍的濃度小於該焊接金屬層(14)中鉍的濃度，該第二焊接擴散層(15)中鉍的濃度小於該焊接金屬層(14)中鉍的濃度。The welding structure of low-temperature solder according to claim 4, wherein the welding metal layer (14) is a tin-bismuth alloy layer containing tin and bismuth, and the second welding diffusion layer (15) is a layer containing tin and bismuth. upper bismuth diffusion layer, the concentration of bismuth in the first welding diffusion layer (13) is less than the concentration of bismuth in the welding metal layer (14), and the concentration of bismuth in the second welding diffusion layer (15) is less than the concentration of bismuth in the welding metal layer (14). 14) in the concentration of bismuth.

如請求項5所述的低溫焊錫的焊接結構，其中，該電極層(16)是一含錫的錫合金電極層。The welding structure of low-temperature solder according to claim 5, wherein the electrode layer (16) is a tin-containing tin alloy electrode layer.

一種焊接結構的製造方法，係依序包含以下步驟：一提供有無鉛焊錫合金焊墊的印刷電路板步驟：提供一焊墊結構(1)，該焊墊結構(1)由下而上至少依序包含：一印刷電路板(10)、一線路層(11)、一IMC層(12)及一無鉛焊錫合金焊墊層(A)；一印刷低溫錫鉍合金錫膏步驟：以一無鉛錫鉍合金錫膏印刷於該無鉛焊錫合金焊墊層(A)的上表面；一置件電子元件步驟：將一電子元件(17)的一電極層(16)疊置於該無鉛錫鉍合金錫膏的上面以形成一焊接結構半成品；一迴焊加熱步驟：將該焊接結構半成品進行加熱，該無鉛錫鉍合金錫膏中的鉍部分往下遷移至該無鉛焊錫合金焊墊層(A)而使該無鉛焊錫合金焊墊層(A)變成一第一焊接擴散層(13)，該無鉛錫鉍合金錫膏中的鉍部分往上遷移至該電極層(16)的下部而使該電極層(16)的下部變成一第二焊接擴散層(15)，該無鉛錫鉍合金錫膏則形成一焊接金屬層(14)，因此獲得一低溫焊錫的焊接結構(100)。 A method for manufacturing a welded structure comprises the following steps in sequence: A step of providing a printed circuit board with lead-free solder alloy pads: providing a pad structure (1), the pad structure (1) from bottom to top at least sequentially comprises: a printed circuit board (10), a circuit layer (11), an IMC layer (12) and a lead-free solder alloy pad layer (A); A step of printing low-temperature tin-bismuth alloy solder paste: printing a lead-free tin-bismuth alloy solder paste on the upper surface of the lead-free solder alloy pad layer (A); A step of placing electronic components: an electrode layer (16) of an electronic component (17) is stacked on the top of the lead-free tin-bismuth alloy solder paste to form a semi-finished product of a welding structure; A re-soldering heating step: heating the semi-finished product of the welded structure, the bismuth part in the lead-free tin-bismuth alloy solder paste migrates down to the lead-free solder alloy pad layer (A) to make the lead-free solder alloy pad layer (A) ) becomes a first solder diffusion layer (13), and the bismuth part in the lead-free tin-bismuth alloy solder paste migrates up to the lower part of the electrode layer (16) so that the lower part of the electrode layer (16) becomes a second solder The diffusion layer (15), the lead-free tin-bismuth alloy solder paste forms a soldering metal layer (14), thereby obtaining a soldering structure (100) of low-temperature soldering.

如請求項7所述的焊接結構的製造方法，其中，該第一焊接擴散層(13)為一含有錫及鉍的下鉍擴散層。The method for manufacturing a welding structure according to claim 7, wherein the first welding diffusion layer (13) is a lower bismuth diffusion layer containing tin and bismuth.

如請求項8所述的焊接結構的製造方法，其中，該焊接金屬層(14)為一含有錫及鉍的錫鉍合金層，該第二焊接擴散層(15)為一含有錫及鉍的上鉍擴散層，該第一焊接擴散層(13)中鉍的濃度小於該焊接金屬層(14)中鉍的濃度，該第二焊接擴散層(15)中鉍的濃度小於該焊接金屬層(14)中鉍的濃度。The method for manufacturing a welding structure according to claim 8, wherein the welding metal layer (14) is a tin-bismuth alloy layer containing tin and bismuth, and the second welding diffusion layer (15) is a layer containing tin and bismuth. upper bismuth diffusion layer, the concentration of bismuth in the first welding diffusion layer (13) is less than the concentration of bismuth in the welding metal layer (14), and the concentration of bismuth in the second welding diffusion layer (15) is less than the concentration of bismuth in the welding metal layer (14). 14) in the concentration of bismuth.