Shadowing Practice: What is SMT (Surface Mount Technology)? PCB Assembly (Part 2) - Learn English Speaking with Video

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1
Welcome to this video where we're going to be looking at what is an SMT
2
and this is using the surface mount technology to assemble PCBs part 2.
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So here we're going to be looking at the PCBA production process.
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We're going to be focusing on these next two elements within the process.
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So there's reflow soldering process and the cleaning process.
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So let's start with the reflow soldering process.
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The circuit board assemblies need to be preheated to activate the flux in the solder paste.
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Then they need to be heated at a higher temperature to reflow the solder.
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A cooling step follows that allows a solder to solidify.
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The The preheating, heating and cooling down cycles in the reflow machine are defined by the thermal profile.
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We'll have a look at that in more detail in the following slides.
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Let's have a look at the cleaning process.
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So the PCB cleaning is the process of removing solder flux residues from the PCB after the SMT process.
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The flux present in the solder paste reacts with the metal oxide during the reflow process
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and prevents further oxidization of the solder metal.
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The byproduct of this reaction is the solder flux residue that gets trapped beneath components and near the undersides of solder balls.
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Let's have a look at the reflow thermal profile.
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We're going to break this down into the separate zones.
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So to start with we have the preheat zone.
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The highest temperature is 2.5 degrees centigrade per seconds in the preheat area.
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Over rising rate will cause solder balling.
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In this image we have the recommended reflow soldering temperature profile.
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We'll be focusing on this throughout this thermal profiling overview.
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The next zone we're going to be focusing on is the soak zone.
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Here we need to keep the temperature within a range of 150 to 210 degrees centigrade
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and the temperature rise rate under 2.5 degrees centigrade per second during the soak zone
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which lasts regularly from 60 seconds to 90 seconds and again we can see that here in this temperature profile.
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The next zone is the reflow zone.
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The peak temperature in the reflowing zone changes in the range of 230 to 255 degrees centigrade.
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Temperature stays above 217 degrees centigrade for 40 to 70 seconds.
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You can see this peak temperature here.
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The final zone is the cool down zone.
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The temperature dropping rate during cool down zone should be kept under 4 degrees centigrade per second.
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Note the curve varies according to the shape of the plate and function of the devices.
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The circumstance parameter is suggested to be 25 plus or minus 2 degrees centigrade by temperature,
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and 45% and 65% by humidity.
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You can see the overall time in this profile is around 270 seconds.
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Let's switch over to the importance of cleaning.
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Cleaning the PCB.
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The solder flux residue, which is trapped between the components of the PCB substrate and the near underside of the solder balls,
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is electrically conductive, as it is made up of ions.
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As PCBs and modules are subjected to an external electric field,
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the diffusing flux residue particles get excited by the momentum transfer of the conducting electrons in the circuit.
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This leads to the particles getting displaced from their position.
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A problem may arise when these particles cause bridging between two parts of the circuit.
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This problem is known as electro migration.
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Now the best practice, let's have a look at that.
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Now there is a no clean solder paste available.
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If possible you should be using this.
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So many of the best performing lead free and lead containing solder pastes today are no cleans.
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They have been designed to solve assembly problems described previously.
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For the vast majority of applications the small amount of residue left by non-clean is not a problem.
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However some assemblers want the performance of no cleans
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but need to clean the no clean residue as they have extreme reliable or cosmetic requirements.
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You can see how clean this no clean solder is in this image here.
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So 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 at all in China.
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So don't forget to like, share and subscribe to our channel and if you hit this little bell symbol
59
that will notify you each time we upload new content.
60
So thanks for listening my name is Paul Adams from I'm SoftEast and I shall see you in the next video.

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אוצר מילים והערות הגייה לשיעור הזה

שיעור הדיבור הזה ברמה C1 מבוסס על הסרטון “What is SMT (Surface Mount Technology)? PCB Assembly”. המילים שחוזרות הכי הרבה: solder, temperature, zone, process, reflow. בסרטון הזה יש 60 משפטים ו-742 מילים לתרגול Shadowing. הדיבור נמשך 5:34. הדובר שומר על קצב יציב של כ-133 מילים בדקה, קצב נוח לתרגול Shadowing. רק 78% מהמילים נמצאות בין 3,000 המילים הנפוצות ביותר באנגלית, כך שאוצר המילים מאתגר.

אוצר מילים מרכזי בסרטון הזה

12 המילים המתקדמות ביותר בסרטון, עם ההגייה והמשמעות שלהן:

מילההגייהמשמעות
solder שם עצם/ˈsɒl.də(ɹ)/לחם
particle שם עצם/ˈpɑɹtək(ə)l/חֶלְקִיק, גַרגִיר
pasta שם עצם/ˈpɑ.stə/פַּסְטָה
soak פועל/soʊk/הִשְׁרָה
substrate שם עצם/ˈsʌbˌstɹeɪt/מַצָּע
assemble פועל/əˈsɛm.bəl/אסף
circumstance שם עצם/ˈsɝ.kəmˌstæns/נסיבות
humidity שם עצם/hjuːˈmɪd.ə.ti/לַחוּת
module שם עצם/ˈmɑd͡ʒul/מוֹדוּל
minus/ˈmaɪ.nəs/פחות, מינוס
subscribe פועל/səbˈskɹaɪb/נִמְנָה
momentum שם עצם/ˌmə(ʊ)ˈmɛntəm/תֶּנַע

Phrasal verbs שתשמעו

מילהמשמעות
check out פועלבדק

משפטים שכדאי לחזור עליהם

משפטים קצרים ושלמים מהסרטון שאפשר להשתמש בהם בשיחה יומיומית:

  • Let's have a look at the cleaning process.
  • Let's have a look at the reflow thermal profile.
  • Let's switch over to the importance of cleaning.

הגייה ששווה לשים לב אליה

הדובר משתמש ב-10 קיצורים וצורות מקוצרות, כמו we're, don't, we'll. אמרו אותם בצורה הקצרה, כפי שאתם שומעים אותם.

  • מילים ארוכות — שימו לב להטעמה: assembler /əˈsɛmb(ə)lɚ/, electrically /ɪˈlɛk.tɹɪk.li/, oxidization /ˌɑksɪdɪˈzeɪʃ(ə)n/, solidify /səˈlɪdɪˌfaɪ/, parameter /pəˈɹæm.ə.tɚ/

צלילים שדוברי עברית מתקשים בהם:

  • /æ/ — פתוח יותר מה-“אֶ” העברית, לא כמו “a” ב-“cup”: parameter /pəˈɹæm.ə.tɚ/, circumstance /ˈsɝ.kəmˌstæns/, activate /ˈæktɪˌveɪt/
  • /r/ — הלשון לא נוגעת בשום מקום, לא ה-“ר” הגרונית: solder /ˈsɒl.də(ɹ)/, residue /ˈɹɛzɪduː/, preheat /pɹiːˈhiːt/, particle /ˈpɑɹtək(ə)l/, electrically /ɪˈlɛk.tɹɪk.li/
  • עיצור קולי בסוף מילה — /b/, /d/, /g/, /z/, /v/ בלי להפוך אותם לאטומים: underside /ˈʌndɚˌsaɪd/, conductive /kənˈdʌktɪv/, diffuse /dɪˈfjuz/, oxide /ˈɑksaɪd/, arise /əˈɹaɪz/

איך לתרגל עם הסרטון הזה

  1. הקשיבו לכל הסרטון פעם אחת בלי לדבר, ורשמו את המילים שאתם לא מכירים.
  2. תרגלו Shadowing משפט אחר משפט במהירות רגילה, וחזרו על כל משפט עד שהקצב שלכם תואם את הדובר.
  3. הקליטו את עצמכם והשוו למקור, תוך תשומת לב למילים כמו solder, particle, pasta.

מהי טכניקת השאדואינג?

שאדואינג היא טכניקת למידת שפה מבוססת מדע שפותחה במקור להכשרת מתורגמנים מקצועיים ופופולרית על ידי הפוליגלוט ד"ר אלכסנדר ארגואלס. השיטה פשוטה אך עוצמתית: אתה מקשיב לאודיו באנגלית ילידית וחוזר עליו בקול רם מיד — כמו צל העוקב אחרי הדובר עם עיכוב של 1–2 שניות בלבד. בניגוד להאזנה פסיבית או תרגילי דקדוק, שאדואינג מכריח את המוח והשרירים בפה לעבד ולשחזר דפוסי דיבור אמיתיים בו זמנית. מחקרים מראים שזה משפר משמעותית את דיוק ההגייה, האינטונציה, הקצב, הדיבור המחובר, הבנת השמיעה ושטף הדיבור — מה שהופך אותו לאחת השיטות היעילות ביותר להכנה לIELTS Speaking ולתקשורת באנגלית בעולם האמיתי.

טכניקת Shadowing: קרא את המדריך המלא שלב אחר שלב →