शैडोइंग अभ्यास: What is SMT (Surface Mount Technology)? PCB Assembly (Part 2) - वीडियो के साथ अंग्रेजी बोलना सीखें
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60 वाक्य
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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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इस पाठ की शब्दावली और बोलने के सुझाव
इस वीडियो में शैडोइंग के लिए 60 वाक्य और 742 शब्द हैं। बोला गया हिस्सा 5:34 लंबा है। वक्ता लगभग 133 शब्द प्रति मिनट की स्थिर गति से बोलता है, जो शैडोइंग के लिए आरामदायक है। केवल 78% शब्द अंग्रेज़ी के 3,000 सबसे आम शब्दों में से हैं, इसलिए शब्दावली कठिन है।
इस वीडियो की मुख्य शब्दावली
वीडियो के 15 सीखने लायक शब्द, उच्चारण और अर्थ के साथ:
| शब्द | उच्चारण | अर्थ |
|---|---|---|
| residue संज्ञा | /ˈɹɛzɪduː/ | शेष, अवशेष |
| pasta संज्ञा | /ˈpɑ.stə/ | पास्ता |
| particle संज्ञा | /ˈpɑɹtək(ə)l/ | कण, ज़र्रा |
| soak क्रिया | /soʊk/ | सोखना |
| mount क्रिया | /maʊnt/ | चढ़ना |
| element संज्ञा | /ˈɛləmənt/ | तत्त्व |
| solve क्रिया | /sɒlv/ | सुलझाना, हल करना |
| symbol संज्ञा | /ˈsɪmbəl/ | प्रतीक, चिह्न |
| reliable विशेषण | /ɹɪˈlaɪəbl̩/ | निष्ठावान |
| requirement संज्ञा | /ɹɪˈkwaɪɹmənt/ | आवश्यकता, अनिवार्यता |
| curve संज्ञा | /kɚv/ | चक्कर, घुमाव |
| migration संज्ञा | /maɪˈɡɹeɪʃ(ə)n/ | प्रवास, माइग्रेशन |
| overview संज्ञा | /ˈoʊ.vɚˌvjuː/ | अवलोकन |
| momentum संज्ञा | /ˌmə(ʊ)ˈmɛntəm/ | संवेग |
| minus | /ˈmaɪ.nəs/ | कम, घटाकर |
ध्यान देने योग्य उच्चारण
वक्ता 10 बार संक्षिप्त रूपों का प्रयोग करता है, जैसे we're, don't, we'll। इन्हें वैसे ही छोटा बोलें जैसा आप सुनते हैं।
- “th” की ध्वनियाँ: thermal /ˈθɜːməl/, beneath /bɪˈniːθ/
- “sh” और “zh” की ध्वनियाँ: migration /maɪˈɡɹeɪʃ(ə)n/, oxidization /ˌɑksɪdɪˈzeɪʃ(ə)n/
- लंबे शब्द — बलाघात सही रखें: momentum /ˌmə(ʊ)ˈmɛntəm/, humidity /hjuːˈmɪd.ə.ti/, parameter /pəˈɹæm.ə.tɚ/, assembler /əˈsɛmb(ə)lɚ/, electrically /ɪˈlɛk.tɹɪk.li/
इस वीडियो से अभ्यास कैसे करें
- पहले बिना बोले पूरा वीडियो एक बार सुनें और जो शब्द नहीं आते उन्हें लिख लें।
- सामान्य गति पर एक-एक वाक्य की शैडोइंग करें और हर वाक्य तब तक दोहराएँ जब तक आपकी लय वक्ता से न मिल जाए।
- अपनी आवाज़ रिकॉर्ड करें और मूल से तुलना करें, ख़ासकर residue, pasta, particle जैसे शब्दों पर ध्यान दें।
शैडोइंग तकनीक क्या है?
शैडोइंग (Shadowing) एक विज्ञान-समर्थित भाषा सीखने की तकनीक है जो मूल रूप से पेशेवर दुभाषिया प्रशिक्षण के लिए विकसित की गई थी। विधि सरल लेकिन शक्तिशाली है: आप मूल अंग्रेज़ी ऑडियो सुनते हैं और तुरंत इसे ज़ोर से दोहराते हैं — जैसे वक्ता की छाया 1-2 सेकंड की देरी से। शोध से पता चलता है कि यह उच्चारण सटीकता, स्वर, लय, जुड़ी हुई ध्वनियाँ, सुनने की समझ और बोलने की प्रवाहशीलता में काफ़ी सुधार करता है।