关于印刷方面理论的描述－中英文版本 [复制链接]

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在表面贴装装配的回流焊接中，锡膏用于表面贴装元件的引脚或端子与焊盘之间的连接。在锡膏印刷工艺中，锡膏、丝印机、锡膏使用方法和印刷工艺过程将影响到印刷质量。印刷锡膏的过程简单描述为将基板放在工作台上，通过机械或真空夹紧定位，并通过定位销或视觉来实现对准，最后来实现锡膏印刷。
Solder paste is applying for the connection between the mount components foot and PCB pads in the SMT assembly. Solder paste, screen printing, use ways, printing process course will decide the printing quality. And usually we describe the simply course of screen printing as firstly we put the stencil onto the worktable, by mechanical or vacuum clamp ways to reality fixed, then by pins or visual ways to reality aiming, and finally to reality screen printing.

1、印刷工艺过程与设备/Screen printing course & equipment
　　在锡膏印刷过程中，印刷机是印刷品质控制的关键。丝印机分为实验室型与生产型两种。其中实验室类型是用来制作产品原型，生产型是用来生产制作。
在手工或半自动印刷机中，锡膏是手工地放在模板/丝网上，这时印刷刮板(squeegee)处于模板的另一端。在自动印刷机中，锡膏是自动分配的。在印刷过程中，印刷刮板向下压在模板上，使模板底面接触到电路板顶面。当刮板走过所腐蚀的整个图形区域长度时，锡膏通过模板/丝网上的开孔印刷到焊盘上。在锡膏已经沉积之后，丝网在刮板之后马上脱开(snap off)，回到原地。这个间隔或脱开距离是设备设计所定的，大约0.020"~0.040"。脱开距离与刮板压力是两个达到良好印刷品质的与设备有关的重要变量。如果没有脱开，这个过程叫接触(on-contact)印刷。非接触(off-contact)印刷用于柔性的金属丝网。
Screen printing equipment is the key of quality control during the printing course. There are laboratory and production types in the current market, lab types used for making production models and production type for producing.
To hand printing or semi-auto printing solder is put by hand onto the stencil or screen while the squeegee locates in the other end and to the auto printing solder is distributed automatically by the machine. The following sentences show the whole course of auto printing. The squeegee press the stencil downward makes the stencil bottom reaching to the PCB top side, and then the solder will be printed onto the PCB pads through the stencil hole when the squeegee passes the whole corrosive area of stencil, after solder finished depositing and stencil will snap off then return to the oriental position. The snap off interval and distance was determined by equipment design precision value that is about 0.020"~0.040". The snap off distance and squeegee press are the two most important variables that concerned with the print quality. We describe the on-contact print as if the PCB isn’t separate from the stencil and the off-contact applies for the flexible stencil.

2、刮板类型/Squeegee types

　　刮板的磨损、压力和硬度决定印刷质量。对可接受的印刷品质，刮板边缘应该锋利和直线。刮板压力低造成遗漏和粗糙的边缘，而刮板压力高或很软的刮板将引起斑点状的印刷，甚至可能损坏刮板和模板或丝网。
The abrasion, press and rigidity of squeegee determine the print quality. It is acceptable if the squeegee edge is sharp and linear. Low pressure will cause missing and rough edge, and high pressure or soft squeegee will cause speckle print even damage the squeegee or stencil.
常见有两种刮板类型/Two squeegee types：
<1>橡胶或聚氨酯刮板：当使用橡胶刮板时，需使用橡胶硬度值为70-90的刮板。
Polyurethane type: we usually use this type squeegee which rubber value should be 70-90 tested by the durometer.
　　<2>金属刮刀：金属刮刀是随着更密间距元件的使用而出现的。它们由不锈钢或黄铜制成，具有平的刀片形状，印刷角度为30~45°。金属刮刀使用较低的压力，从而避免从开孔中挖出锡膏；金属刮刀不像橡胶刮板那样容易磨损，其成本比橡胶刮板贵得多，并可能引起模板磨损。
Metal squeegee: now we introduce another type squeegee—metal squeegee which satisfies for the demands of the appearance of more small pitch components and it is made of stainless steel or brassiness. The metal squeegee has the even shape and its print angle is about 30~45°. It is usually use the lower pressure to avoid excavating the paste from the stencil and other advantage is that less abrasion than the polyurethane type but more expensive and it is also causes the stencil abrasion.

3、模板类型/Stencil Type
　　印刷品质变量包括模板孔壁的精度和光洁度以及模板宽度与厚度的适当的纵横比。推荐的纵横比为1.5，主要是防止模板阻塞。一般情况如果纵横比小于1.5，锡膏会保留在开孔内。除了纵横比之外，如IPC-7525《模板设计指南》所推荐的，还要有大于0.66的面积比(焊盘面积除以孔壁面积)。
The print quality variable includes the hole precision & clearance and the other important variable is the aspect ratio of stencil width and thickness, and the commendatory value is 1.5 to preventing from stencil block. Usually if the ratio is less than 1.5 the paste will stay in the hole, besides, the area ratio of pad and hole-wall more than 0.66 is more important recommended by the IPC-7525/<<The User Guide for Stencil Design>>.
　　开孔壁的光洁度和精度由制作开孔的工艺过程控制。三种常见的制作模板的工艺为：化学腐蚀、激光切割和铸成型工艺。
The hole-making process course control the hole precision & clearance and the three ways of making stencil are chemically etched, laser-cut, electroformed.


4、化学腐蚀模板/Chemically Etched Stencil
　　金属模板和柔性金属模板是使用两个阳性图形通过从两面的化学研磨来蚀刻的。在这个过程中，蚀刻不仅按设计的垂直方向进行，同时在横向进行。
Metal & flexible stencil was etched by two positive graphics through two sides and the erodent was done in the direction of horizontal and perpendicularity.  
　　
5、激光切割模板/Laser-cut Stencil
　　激光切割是另一种减去(subtractive)工艺。模板直接根据Gerber数据制作，因此开孔精度可以得到改善。数据也可按需要调整以便于改变尺寸。良好的过程控制也会改善开孔精度。激光切割模板的另一个优点是孔壁可成锥形。化学蚀刻的模板也可以成锥形，但是如果只从一面腐蚀，开孔尺寸可能太大。
The laser-cut stencil is a subtractive process which is basing the Gerber data that is propitious to improve the hole-making precision, besides we can adjust the stencil by changing the Gerber data. And another advantage is that the hole-wall shape is taper. Maybe the chemically etched can form the taper but the hole dimension maybe too big if only etch from one side.
　　激光切割可以制作出小至0.004"的开孔宽度，精度达到0.0005"，因此很适合于超密间距(ultra-fine-pitch)的元件印刷。
The minimum hole width can reach to less than 0.004” and precision is 0.0005” if we use the laser-cut way so the laser-cut is adaptable for the ultra-fine-pitch print.
激光切割的模板也会产生粗糙的边缘，因为在切割期间汽化的金属变成金属渣。这可能引起锡膏阻塞。更平滑的孔壁可通过微蚀刻来产生。
The laser-cut will also produce the rough fringe because the metal gas status will be turned into the metal dregs during the course of cutting, and the dregs will also hold the paste. We may get the smooth hole by the hand of micro-etched ways.

6、铸成型模板/Electroformed Stencil

　　制作模板的第三种工艺是电铸成型。在这个工艺中，镍沉积在铜质的阴极心上以形成开孔。
The third ways of making stencil is electroform. Hole forming by the way of nickel deposit onto the copper cathode.

二、锡膏/Paste

1、免洗錫膏--RMA(Rosin Mild Activated)
特点/Specialties：
〈1〉良好的湿润性/Good capability of wetness；
〈2〉均匀的扩散性/Uniform dispense capability；
〈3〉极佳的印刷性/Well capability of printing；
〈4〉固化后的助焊剂残渣具有极佳的电气信赖性/Good electric reliability of flux after reflow；
〈5〉极佳的表面绝缘抵抗/Well capability of surface insulated；
〈6〉无桥接/No solder bridge；
〈7〉良好焊接性能/Good solder capability；
〈8〉高水溶液抵抗性能/High water-liquid resistance capability；



2、免洗錫膏--RA(Rosin Activated)
特性/Specialties：
〈1〉良好的湿润性/Good capability of wetness；
〈2〉均匀的扩散性/Uniform dispense capability；
〈3〉助焊剂活性高/High activities of flux.
〈4〉固化后的助焊剂残渣具有极佳的电气信赖性/Good electric reliability of flux after reflow；
〈5〉极佳的表面绝缘抵抗/Well capability of surface insulated；
〈6〉无桥接/No solder bridge；
〈7〉良好焊接性能/Good solder capability；
〈8〉高水溶液抵抗性能/High water-liquid resistance capability；


3、无鉛锡膏/Lead-free Paste
特性/Specialties：
〈1〉鉛含量< 0.1 %；Lead content<0.1%
〈2〉多种合金供客户选择/Various metal can be choiced；
〈3〉良好的湿润性/Good capability of wetness；
〈4〉均匀的扩散性/Uniform dispense capability；
〈5〉良好焊接性能/Good solder capability；
〈6〉固化后的助焊剂残渣具有极佳的电气信赖性/Good electric reliability of flux after reflow；


4、产品测试特性值/The test value of specialties：


三、锡膏的正确使用/The correct ways of using paste

1、锡膏使用与保管的基本原则/The use & storage principles of paste：

<1>基本原则是尽量与空气少接触，越少越好。锡膏与空气长时间接触后，会造成锡膏氧化、助焊剂比例成分失调。产生的后果是：锡膏出现硬皮、硬块、难熔并产生大量锡球等。
The basic principle is less contact with the air. It will cause the paste oxidation and lose flux ratio balance if it is exposed for long-time. So it will result in rigidity skin & block and solder balls etc.
<2>锡膏的保存最好以密封形态存放在恒温、恒湿的冰箱内，保存温度为2～8 ℃。锡膏从冰箱中取出时，应在其密封状态下，回到室温后再开封，然后放在搅拌机上充分搅拌，再加到网版上使用。
The best way of keeping solder paste is put it into the refrigerator under the lower temperature of 2～8℃ with the sealed forms. And then take it from the refrigerator until the solder paste is back to the normal temperature with the sealed forms the operator may open it and use.


2、锡膏多次使用时的注意事项/Attentions for more use
  <1>开盖时间要尽量短，一次取出够用的焊膏后，应立即将内盖盖好。不要取一点用一点，频繁开盖或始终将盖子敞开着。
  The operator should assure a shorter open time and make the paste be in good sealed status after we have taken sufficient solder paste once. On the other hand it is a wrong way of opening the cover frequently or not covering the solder paste.
<2>取出锡膏后，将内盖立即盖好，用力下压，挤出盖子与焊膏之间的全部空气，使内盖与焊膏紧密接触。确信内盖压紧后，再拧上外面的大盖。
  After have taken the solder paste out the operator should assure the inner-cover be in the good status and press it forcedly to push all air between cover and solder paste to making them contact compactness and then tweak the out-cover.
<3>取出的锡膏要尽快实施印刷使用。
The operator should use the solder paste quickly after it has been taken out.
  <4>已取出的多余焊膏的处理。
全部印刷完毕后，剩余的焊膏应尽快回收到一个专门的回收瓶内，并如同注意事项2与空气隔绝保存。绝对不要将剩余焊膏放回未使用的焊膏瓶内！因此在取用焊膏时要尽量准确估计当班焊膏的使用量。
As soon as finishing screen printing the rest of solder paste should be back into a special vast and the attentions according to the 2nd notes. Don’t mix the rests with the untapped solder past so the operator should estimate correctly the solder paste use volume.
<5>出现问题的处理/Problem treat with。
若已出现焊膏表面结皮、变硬时，千万不要搅拌！务必将硬皮、硬块除掉，剩下的焊膏在正式使用前要作一下试验，看试用效果如何，若不行，就只能报废了。
Don’t mix the solder paste when the operator find it has been rigidity skin & block status and we must remove it.

四、印刷前如何判断锡膏粘度/How to judge the solder paste adhibit.
我们在进行锡膏印刷前应对锡膏进行一定的检测。如果没有专用设备也可以用以下的方法检查一下。
    首先将已解冻的锡膏用刮刀搅拌五到八分钟（不同品牌的锡膏搅拌时间可能有所不同）。然后用刮刀从瓶内挑起一些到离瓶十厘米的地方，最后观察下降的情形，如果慢慢的很均匀的向下掉则表示该锡膏粘度适中可以使用。如果在刮刀上不下来则表示粘度太大，若大块大块的掉下来则说明该粘度太小也不能使用。
We should judge the adhibit of solder paste before screen printing by automatic machine or by hand.
Firstly mill the solder paste with scraper about 5~8 minutes(different time for different brand solder paste) then pick some solder paste 10CM above the vast to observe the descent status, if it is uniform shows the adhibit is good for using, if it is the other status shows the adhibit is badly.
五、锡膏印刷缺陷分析/Printing Defects Analysis