Pratique du Shadowing: What is SMT (Surface Mount Technology)? PCB Assembly (Part 2) - Apprendre l'anglais à l'oral avec la vidéo
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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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Vocabulaire et conseils d’expression pour cette leçon
Cette vidéo contient 60 phrases et 742 mots à répéter en shadowing. La partie parlée dure 5:34. Le locuteur parle à un rythme régulier d’environ 133 mots par minute, confortable pour le shadowing. Seuls 78 % des mots font partie des 3 000 mots les plus courants en anglais, le vocabulaire est donc exigeant.
Vocabulaire clé de cette vidéo
15 mots de la vidéo à retenir, avec leur prononciation et leur sens :
| Mot | Prononciation | Sens |
|---|---|---|
| flux nom | /flʌks/ | décapant |
| residue nom | /ˈɹɛzɪduː/ | résidu |
| thermal adjectif | /ˈθɜːməl/ | thermique |
| pasta nom | /ˈpɑ.stə/ | pâtes, pâtes alimentaires |
| particle nom | /ˈpɑɹtək(ə)l/ | particule |
| trap nom | /tɹæp/ | piège, collet |
| component nom | /kəmˈpoʊ.nənt/ | composant |
| soak verbe | /soʊk/ | tremper |
| vast adjectif | /væst/ | vaste, immense |
| mount verbe | /maʊnt/ | monter, grimper |
| element nom | /ˈɛləmənt/ | élément |
| solve verbe | /sɒlv/ | résoudre, régler |
| define verbe | /dɪˈfaɪn/ | déterminer |
| symbol nom | /ˈsɪmbəl/ | symbole |
| slide nom | /ˈslaɪ̯d/ | toboggan, glissoire |
Les verbes à particule que vous entendrez
| Mot | Prononciation | Sens |
|---|---|---|
| cool down verbe | /kuːl ˈdaʊn/ | se refroidir, refroidir |
| check out verbe | mater, regarder |
Prononciation à surveiller
Le locuteur utilise 10 contractions et formes réduites, comme we're, don't, we'll. Prononcez-les sous leur forme courte, telles que vous les entendez.
- Les sons « th »: thermal /ˈθɜːməl/, beneath /bɪˈniːθ/
- Les sons « sh » et « zh »: migration /maɪˈɡɹeɪʃ(ə)n/, oxidization /ˌɑksɪdɪˈzeɪʃ(ə)n/
- Mots longs — placez bien l’accent: momentum /ˌmə(ʊ)ˈmɛntəm/, humidity /hjuːˈmɪd.ə.ti/, parameter /pəˈɹæm.ə.tɚ/, assembler /əˈsɛmb(ə)lɚ/, electrically /ɪˈlɛk.tɹɪk.li/
Comment s’entraîner avec cette vidéo
- Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
- Répétez phrase par phrase à vitesse normale, en reprenant chacune jusqu’à ce que votre rythme corresponde à celui du locuteur.
- Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme flux, residue, thermal.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.