Shadowing Practice: What is SMT (Surface Mount Technology)? PCB Assembly (Part 2) - Learn English Speaking with Video
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Welcome to this video where we're going to be looking at what is an SMT
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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
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that will notify you each time we upload new content.
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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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Woordenschat en spreektips bij deze les
Deze video bevat 60 zinnen en 742 woorden om na te spreken. Het gesproken deel duurt 5:34. De spreker praat in een gelijkmatig tempo van ongeveer 133 woorden per minuut, prettig om te shadowen. Slechts 78% van de woorden hoort bij de 3.000 meest gebruikte Engelse woorden, dus de woordenschat is pittig.
Belangrijke woorden in deze video
15 woorden uit de video die het leren waard zijn, met uitspraak en betekenis:
| Woord | Uitspraak | Betekenis |
|---|---|---|
| flux zelfstandig naamwoord | /flʌks/ | voortdurende wijziging |
| pasta zelfstandig naamwoord | /ˈpɑ.stə/ | deegwaren, pasta |
| particle zelfstandig naamwoord | /ˈpɑɹtək(ə)l/ | deeltje, partikel |
| trap zelfstandig naamwoord | /tɹæp/ | val |
| component zelfstandig naamwoord | /kəmˈpoʊ.nənt/ | onderdeel, component |
| soak werkwoord | /soʊk/ | doorweken |
| vast bijvoeglijk naamwoord | /væst/ | enorm |
| mount werkwoord | /maʊnt/ | beklimmen |
| element zelfstandig naamwoord | /ˈɛləmənt/ | element |
| solve werkwoord | /sɒlv/ | oplossen |
| define werkwoord | /dɪˈfaɪn/ | bepalen, determineren |
| symbol zelfstandig naamwoord | /ˈsɪmbəl/ | symbool |
| slide zelfstandig naamwoord | /ˈslaɪ̯d/ | glijbaan, schuifaf |
| reliable bijvoeglijk naamwoord | /ɹɪˈlaɪəbl̩/ | betrouwbaar, zeker |
| requirement zelfstandig naamwoord | /ɹɪˈkwaɪɹmənt/ | vereiste, plicht |
Phrasal verbs die je zult horen
| Woord | Uitspraak | Betekenis |
|---|---|---|
| cool down werkwoord | /kuːl ˈdaʊn/ | afkoelen, koelen |
| check out werkwoord | onderzoeken |
Uitspraak om op te letten
De spreker gebruikt 10 samentrekkingen en verkorte vormen, zoals we're, don't, we'll. Spreek ze kort uit, zoals je ze hoort.
- De “th”-klanken: thermal /ˈθɜːməl/, beneath /bɪˈniːθ/
- De klanken “sh” en “zh”: migration /maɪˈɡɹeɪʃ(ə)n/, oxidization /ˌɑksɪdɪˈzeɪʃ(ə)n/
- Lange woorden — let op de klemtoon: momentum /ˌmə(ʊ)ˈmɛntəm/, humidity /hjuːˈmɪd.ə.ti/, parameter /pəˈɹæm.ə.tɚ/, assembler /əˈsɛmb(ə)lɚ/, electrically /ɪˈlɛk.tɹɪk.li/
Zo oefen je met deze video
- Luister de hele video één keer zonder te spreken en noteer de woorden die je niet kent.
- Spreek zin voor zin na op normale snelheid en herhaal elke zin tot je ritme gelijk is aan dat van de spreker.
- Neem jezelf op en vergelijk met het origineel; let daarbij op woorden als flux, pasta, particle.
Wat is de Shadowing-techniek?
Shadowing is een wetenschappelijk onderbouwde taalleermethode die oorspronkelijk is ontwikkeld voor professionele tolkentraining en gepopulariseerd door polyglot Dr. Alexander Arguelles. De methode is eenvoudig maar krachtig: je luistert naar native Engelse audio en herhaalt het onmiddellijk hardop — als een schaduw die de spreker volgt met slechts 1–2 seconden vertraging. In tegenstelling tot passief luisteren of grammaticadrills, dwingt shadowing je hersenen en mondspieren om echte spraakpatronen tegelijkertijd te verwerken en te reproduceren. Onderzoek toont aan dat het de uitspraaknauwkeurigheid, intonatie, ritme, verbonden spraak, luisterbegrip en spreekvaardigheid aanzienlijk verbetert — waardoor het een van de meest effectieve methoden is voor IELTS Speaking-voorbereiding en echte Engelse communicatie.