跟读练习: What is SMT (Surface Mount Technology)? PCB Assembly (Part 1) - 通过视频学习英语口语
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Music Welcome to the next video in the series of PCBs.
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Here we're going to be looking at what is an SMT.
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So using a surface mount technology to assemble PCBs Part 1.
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Surface Mount Technology Overview.
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Now, Surface Mount Technology, which is the SMT, is a method for producing electrical circuits in which the components are mounted
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or placed directly onto the surface of printed circuit boards or PCBs.
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An electrical device that is soldered to the PCB is called a Surface Mount Device or an SMD for short.
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By employing SMT, the production process speeds up
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but the risk of defects also increases due to the component miniaturization and to the denser packing of boards.
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In these conditions, detection of failures has become critical for any SMT manufacturing process.
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Let's have a look at the PCBA production process.
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So manufacturing PCBs with SMA techniques.
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Manufacturing of printed circuit boards with an automated surface mount assembly,
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or SMA line, consists of the following sequence of operations.
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Solder paste application Component placement reflow soldering, cleaning and electrical test In this video,
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we will concentrate on the first two steps in this process.
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So we'll look at preassembly steps.
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So the PCB design and manufacture.
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Once the PCB has been designed and the components selected, it is time to get the PCB produced and the components ordered.
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PCBs that are populated on a serviceman assembly line are normally produced in panel formats, as shown on the right hand side here.
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The SMDs come packaged in different methods from trays for larger components and on tape bound on a reel for smaller components.
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All the SMDs need to be sourced and made ready to load into the manufacturing line machines.
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SodaPaste application Let's have a look at the solder paste application process.
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So once the PCB is loaded into the machine, the stencil is positioned over the panels.
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Solder paste is then added in front of the squeegee.
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Let's have a look at that in a diagram format.
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So we can see here the stencil is lowered onto the PCB, the squeegee is in position,
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and the solder paste loaded just before the squeegee.
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The squeegee lowers onto the stencil such that it is applying a very specific amount of pressure.
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The squeegee moves along the length of the stencil while the solder paste is deposited into the stencil apertures.
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And you can see that in this image here,
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where the squeegee has completed its journey and left the solder deposits in the stencil apertures.
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At the end of the travel, the squeegee raises up and the stencil is separated from the panels.
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That is depicted here in this image.
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You can see the stencil is raised leaving the soda paste on the correct positions on the pads.
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Solder paste issues.
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So this first one is the acceptable deposit onto a pad.
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This is what it should be looking like.
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Some of the issues that could follow are: Slumped deposit of solder paste onto the pad, which just looks like it's just dumped on.
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Scavenged deposits of solder, and this is where the middle has been scooped out, and you can see that here.
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Ridging is where a solid paste is connected between Two pads.
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The last one we're going to look at is peaking or dog ears effect.
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And you can see that depicted here.
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So component placement process Let's have a look at that in the PCB design and manufacture.
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So basic placement sequence generally includes board indexing,
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board registration, fiducial vision alignment, component pickup component centering or vision inspection,
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component placement and board indexing, and automated optical inspection, Component pickup.
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component centering and vision inspection, component placement are repeated for each component.
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And you can see an example of a component placed on the wet soda pads here.
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Thank you.
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Let's have a look at PCB positioning.
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and the PCB positioning method.
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Through the process of board indexing, The PCP is loaded to the appropriate position.
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Fiducial marks provide common measurable points for all steps in the assembly process.
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The three main types of fiduciary marks are: 1.
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Panel.
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This is a global fiducial mark on a multiple printed circuit board fabrication panel
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that are located outside the parameters of the end product printed circuit boards.
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You can see an example of that here.
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2. Global.
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These are fiduciary marks used to locate the position of all the features on an individual printed circuit port.
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Again, this is shown here. And three, local.
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These are fiduciary marks or marks used to locate the position of an individual allowance pattern
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or component that may require more precision location such as a QFP.
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and again you can see that here in this image Pick and place types.
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Let's have a look at the chip shooter type.
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Now chip shooters are generally fast.
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They can range between 20 ,000 and 80 ,000 placements per hour
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and can even range up to 100 ,000 placements per hour with relatively low accuracy, generally in a range of 70 microns.
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As a result, chip shooters are not generally used for placing a active components which require better accuracy.
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There are three major types of chip shooters Stationary turret overhead gantry and revolver head.
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You can see an example of a chip shooter in this picture here.
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Let's have a look at a flexible placer type Now comparing to chip shooters, these are flexible places are slow.
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and they range between 6 ,000 to 40 ,000 placements per hour.
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But they have a high accuracy, as low as 25 microns.
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As a result, flexible placers are used to place complex and high I -O active components,
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such as QFPs, as high -performance I -O components generally require higher accuracy.
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There are three major types of flexible placer, Split axes.
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Thank you.
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Vacuum nozzles and grips.
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Let's have a look at vacuum nozzles.
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Vacuum nozzles are commonly used for handling all the components during the placement operations.
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There are a variety of vacuum nozzle sizes for different component sizes.
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For handling small components, positive pressure is often supplied in addition to vacuum at the moment of placement
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so that the component will be completely released from the nozzle.
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You can see a selection of vacuum nozzles in this image here.
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You can see the different sizes for the vacuum pickup.
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We also have mechanical grips.
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Self -centering mechanical grippers allow simultaneous pickup and automatic centering without a need for vacuum.
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A pair of tweezer type grippers would hold the part while centering it along one axis.
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Vision inspection.
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Upward facing vision system.
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The vision inspection part of the process checks the critical components have been picked correctly.
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their orientation and other features such as Pin 1 location.
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All of this data is then fed into the machine to
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ensure the device is placed into position with the highest accuracy possible.
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Inline Automated Optical Inspection or AOI.
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AOI is an automated visual inspection for printed circuit board manufacture
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where a camera autonomously scans the device under test for both catastrophic failure, in other words missing component,
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and quality defects such as fillet size or shape of component skew.
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And this is what that looks like.
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See the difference between these two.
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One is up facing and the other is down facing or in this case, top and bottom vision.
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Don't forget to check out our other videos in this PCB series
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and you can contact us if you need any help with your projects in China.
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So don't forget to like, share and subscribe to our channel.
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And if you hit this little bell symbol that will notify you of every new content that we upload.
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So thanks for listening, my name is Paul Adams and I shall see you in the next video.
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本课的词汇与口语要点
这节 C1 级别的口语课以视频“What is SMT (Surface Mount Technology)? PCB Assembly”为素材。 视频中反复出现的词有：component, Pcb, placement, board, solder。 这段视频共有 108 个句子、1290 个单词可供跟读。 讲话部分时长为 10:18。 说话人语速平稳，每分钟约 125 个词，很适合跟读。 只有 72% 的单词属于英语最常用的 3,000 词，词汇难度较高。
视频中的重点词汇
视频中最难的 15 个单词，附发音和释义：
| 单词 | 发音 | 释义 |
|---|---|---|
| solder 名词 | /ˈsɒl.də(ɹ)/ | 焊料 |
| placement 名词 | /ˈpleɪ̯smənt/ | 放置, 安置 |
| pasta 名词 | /ˈpɑ.stə/ | мянфан, 意大利麵 /意大利面 |
| stencil 名词 | /ˈstɛnsəl/ | 漏字版, 蠟紙 /蜡纸 |
| vacuum 名词 | /ˈvæ.kjuːm/ | 真空 |
| squeegee 名词 | /ˈskwiˌd͡ʒi/ | 刮刀刮水刷 |
| shooter 名词 | /ˈʃuːtəː/ | 射手 |
| automate 动词 | /ˈɔ.təˌmeɪt/ | 自動化 /自动化 |
| fiduciary 名词 | /fəˈduːʃ.i.eɹ.i/ | 受託人 /受托人, 受託者 /受托者 |
| pad 名词 | /pæd/ | 墊 /垫, 墊子 /垫子 |
| aperture 名词 | /ˈæp.ɚˌt͡ʃʊɹ/ | 孔 |
| depict 动词 | /dɪˈpɪkt/ | 描繪 /描绘, 描述 |
| micron 名词 | /ˈmaɪkɹɒn/ | 微米 |
| defect 名词 | /ˈdiːfɛkt/ | 缺點 /缺点, 問題 /问题 |
| soda 名词 | /ˈsoʊdə/ | 蘇打 /苏打, 碳酸鈉 /碳酸钠 |
视频中出现的短语动词
| 单词 | 发音 | 释义 |
|---|---|---|
| check out 动词 | 退房 | |
| speed up 动词 | /spiːdˈʌp/ | 加速, 加快 |
视频中的语法
说话人最常用的结构，并附上视频中的原话：
| 结构 | 视频中的用法 |
|---|---|
| “used to” used to + 动词 — 过去的习惯或状态，现在已不再如此 | used to locate |
| 被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的 | are mounted · is soldered · has been designed |
| 现在完成时 have/has + 过去分词 — 过去发生但与现在仍有关联的事 | has become · has been designed · has completed |
需要注意的发音
说话人用了 5 次缩略和弱读形式，例如 don't, we're, we'll。请按听到的简短形式来说。
- “sh” 和 “zh” 音: shooter /ˈʃuːtəː/, fiducial /fəˈd(j)uːʃəl/, fiduciary /fəˈduːʃ.i.eɹ.i/, fabrication /fæbɹɪˈkeɪʃən/, measurable /ˈmɛʒəɹəbəl/
- 长单词——注意重音位置: fiduciary /fəˈduːʃ.i.eɹ.i/, fabrication /fæbɹɪˈkeɪʃən/, measurable /ˈmɛʒəɹəbəl/, simultaneous /ˌsaɪ̯.məlˈteɪ̯.ni.əs/, parameter /pəˈɹæm.ə.tɚ/
中文母语者容易读错的音：
- /v/ — 不要读成 /w/，上齿轻触下唇: vacuum /ˈvæ.kjuːm/, revolver /ɹɪˈvɒl.vɚ/, scavenge /ˈskæv.ɪndʒ/, overhead /ˈəʊvəˌhɛd/
- 词尾辅音 — 要读清楚，后面不要加元音: placement /ˈpleɪ̯smənt/, automate /ˈɔ.təˌmeɪt/, locate /ˈloʊˌkeɪt/, pad /pæd/, depict /dɪˈpɪkt/
- /r/ 和 /l/ 的区别: solder /ˈsɒl.də(ɹ)/, placer /ˈpleɪsə(ɹ)/, measurable /ˈmɛʒəɹəbəl/, revolver /ɹɪˈvɒl.vɚ/, reel /ˈɹiːl/
如何用这段视频练习
- 先完整听一遍视频，不要开口，记下不认识的单词。
- 用正常速度逐句跟读，每句重复到你的节奏与说话人一致为止。
- 录下自己的声音并与原声对比，特别注意 solder, placement, pasta 这类单词。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。