シャドーイング練習: What is SMT (Surface Mount Technology)? PCB Assembly (Part 2) - 動画で英語スピーキングを学ぶ
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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.
このレッスンについて
「What is SMT (Surface Mount Technology)? PCB Assembly (Part 2)」を使って、シャドーイングで英語を練習しましょう。
毎日15〜30分の練習で、IELTSスピーキングへの自信と実践的な英会話力が身につきます。
シャドーイングとは？英語上達に効果的な理由
シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。