Prática de Shadowing: PCB Inspection Methods & Common PCB Defects - Aprenda a falar inglês com vídeo
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This is the next video in the PCB series.
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Here we're going to be looking at printed circuit board assemblies and the inspection methods and common defects.
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So checking solder paste process.
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There are a number of points to check for with the solder paste process.
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1. We need to be looking at the paste stencil alignment.
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If an automatic solder paste machine is being used, the general method is to use a camera to determine the position of the PCB by checking for the dooshals,
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alignment dots on the PCB.
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We covered this in a previous video.
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The manual method of setting up the stencil is to align the stencil with the PCB printed pads.
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then set the clamp stops to hold the PCB in the correct place.
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What to check for?
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Well you need to check the solder paste is correctly aligned to all of the pads on the PCB.
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Over on the right here we can see three images.
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The top image, which is good, shows that all of the paste is aligned with the pads.
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The middle shows some errors we can see here, slight misalignment and one bridge between two solder plates.
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The bottom one is just a mess, i.e. the ugly looking thing, with solder all over the place.
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Two, the squeegee speed and pressure.
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The squeegee speed should not be too fast that the paste does not roll as it moves across the stencil
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or too slow
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that the print cycle time does not keep up with the manufacturing line The blade pressure is usually set
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so that no paste remains on the stencil behind the squeegee
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Higher pressures will not only damage the stencil but also shear thin the paste
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to such an extent that the flux will separate from the metal and problems such as paste sticking to the blade,
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lack of tack at placement or poor solderability will occur further down the assembly line.
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What to check for?
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We need to check for solder paste is not left on the stencil after a pass
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and that all the solder pads have adequate paste deposited.
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Again on the right hand side here, going from the top left, 1, the alignment gasket of apertures to the pad.
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2, we need to check the squeegee motion, things paste so it flows into the apertures.
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3, bottom left, paste, recovers, stiffens up.
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And of 4, the bottom right, the stencil separates from PWB, paste deposits release from the stencil into the pads.
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Now let's have a look at the five major issues with pick and place machines.
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Fault number one, loss of vacuum.
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What to check for?
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Or primary process set up areas to check.
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Is nozzle damaged and will not sit flush against the component's surface?
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Or damaged vacuum hoses or a vacuum system?
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Fault number two, short or worn nozzles.
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What to check for?
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Short nozzles will result in components not being placed correctly resulting in component shift and movement.
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Worn nozzle tips result in loss of vacuum and you will see components being dropped.
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Measure nozzles against dimensional acceptance.
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Thought number 3.
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Sticking nozzles.
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What to check for?
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Damaged nozzles that do not fit correctly into their holders.
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old and non-maintained nozzles.
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On the right hand side there you can see the top image showing the nozzle area.
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Make sure these are not worn or damaged in any way.
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The bottom image just shows a variety of different nozzles that can be used.
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Thought number four, higher than normal reject rates at inspection.
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What to check for components were not presented to the nozzle in a consistent position,
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poor nozzle alightening from degradation of reflective discs or nozzle face over time,
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dirty reflective discs or nozzle face, a poor quality of reflective disc or nozzle face,
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nozzle height is incorrect, And finally, stuck nozzles from part height incorrect setting program.
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Nozzle worn beyond their tolerances or incorrect length tolerance on nozzles.
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Fault number 5.
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Component and circuit board damaged caused by ESD.
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What to check for?
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Ensure nozzles are manufactured from electrostatic dissipating materials.
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manufacturing manufacturers data sheet for this.
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What to check for with incorrect wave solder profile.
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Default here is bridging.
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What to check for?
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Well the primary process setup areas to check are conveyor speed too slow or other incorrect solder wave settings,
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time Overheat is too long causing flux to be burnt off.
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Dwell time is too long causing the flux to burn off before exiting the wave.
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Top side board temperature too low.
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Not enough flux applied to the flux activity is too low.
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You can see here in this image solder bridging between two points.
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the incorrect wave soldering profile issue, the fault being insufficient solder on topside fillet.
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What to check for?
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Conveyor speed is too low.
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Check the time over preheat too long, causing the flux to be burned off.
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Dwell time is too long, causing flux to be destroyed before exiting the wave.
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The conveyor speed is too fast.
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Dwell time is too short.
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topside board temperature too high for flux causing it to burn off before the wave, not enough flux or the flux is not active enough,
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solder temperature too low it cools in the barrel before it reaches the topside,
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and wave height too low in one or both waves so the solder does not contact the board properly.
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In this image it clearly shows there is insufficient solder to make this a good contact.
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Another incorrect wave solder profile issue
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so the fault here is insufficient solder bottom side fillet conveyor
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speed is too slow time over preheat too long causing the
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flux to be burnt off dwell time is too long causing flux to be destroyed before it exits the wave.
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Bottom side board temperature is too high causing flux to be burnt off before the wave
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and not enough flux or flux activity.
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The wave height is too low on one or both waves.
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And we can see here on the right hand side we've got problems with that connector.
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On the bottom is insufficient solder where this component is placed.
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Another incorrect wave solder profile issue, the fault here, is de-wetting or non-wetting.
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What to check for?
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Usually the board related due to contamination on the surface of the pads.
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Solder temperature too low, solder wave height too low, contaminated flux or contaminated solder.
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Or the conveyor speed is too high or too low.
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And again, we can see examples here of solder de-wetting or non-wetting in the bottom instance.
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Another incorrect wave solder profile issue is solder voids.
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Now what to check for here.
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Topside or overall board temperature is too low in trapping moisture that is outgassed at the wave.
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Entrapped fluid by component in through hole.
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Chemical contaminants not removed during PC fabrication process.
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Contamination in the hole.
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Top side of the hole covered by component body or flashing.
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You can see an example of a solder void here.
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Another fault is solder skip.
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Now what to check for?
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Conveyor speeds too fast.
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so the dwell was too short in the wave.
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Make sure the chip or turbine wave is turned on.
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Not enough flux for the solder to bond.
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Wave height too low on one or both waves.
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You can clearly see here this pad has no solder at all.
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Another fault is icicles or flags or horns.
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Now what to check for?
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conveyor speeds too slow.
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Time over preheat too long causing flux to burn off.
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Dwell time too long causing flux to be destroyed before exiting to the wave.
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Solar temperature too low, not enough flux.
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The use of nitrogen will help prevent icicles.
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You can see a good example here of what we're talking about when we mention solar flags.
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Another fault is solder on mask Poor flux application Flux and resist incompatibility Poor cure of the solder mask
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Preheat temperatures too high Solder temperature too high This image just shows the solder on the mask itself
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another fault is rough or disturbed solder check conveyor for vibration or jerky motion
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removal of the board prior to the solder solidifying solder temperature too low conveyor speed too high and wave run uneven
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you can see what we're talking about with rough solder in this image
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just to summarize here's an image of some common faults I'm
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just going to go through these with the top left moving to the right
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so we've got lifted component we've got tombstone effect
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wrong polarity upside down mounting in the second row we have a missing component
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we have that missing solder that we saw earlier we have a lifted lead
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we've got that solder bridging again
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on the bottom row we've got billboarding then we have shifted or twisted component we have our solder flags again
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and that solder void
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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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Don't forget to like, share and subscribe to our channel.
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And you see there's a little bell symbol.
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If you hit that, you'll get a notification every time we upload new content.
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Thanks for listening.
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My name is Paul Adams from South East and I shall see you in the next video.
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Vocabulário e dicas de fala para esta lição
Este vídeo tem 140 frases e 1559 palavras para praticar shadowing. A fala dura 12:27. O falante mantém um ritmo estável de cerca de 125 palavras por minuto, confortável para o shadowing. Apenas 76% das palavras estão entre as 3.000 mais comuns do inglês, por isso o vocabulário é exigente.
Vocabulário principal deste vídeo
15 palavras do vídeo que vale a pena aprender, com pronúncia e significado:
| Palavra | Pronúncia | Significado |
|---|---|---|
| flux substantivo | /flʌks/ | fluxo |
| pasta substantivo | /ˈpɑ.stə/ | massa, macarrão |
| component substantivo | /kəmˈpoʊ.nənt/ | componente |
| incorrect adjetivo | /ˌɪn.kəˈɹɛkt/ | incorreto |
| dwell verbo | /dwɛl/ | habitar, morar |
| exit substantivo | /ˈɛɡzət/ | saída |
| vacuum substantivo | /ˈvæ.kjuːm/ | vácuo |
| mask substantivo | /mæsk/ | máscara |
| correctly advérbio | /kəˈɹɛk(t).li/ | corretamente |
| void adjetivo | /vɔɪd/ | vazio, vazia |
| alignment substantivo | /əˈlaɪn.mənt/ | alinhamento |
| align verbo | /əˈlaɪn/ | alinhar-se, alinhar |
| reflective adjetivo | /ɹɪˈflɛktɪv/ | reflexivo |
| circuit substantivo | /ˈsɝ.kɪt/ | circuito, volta |
| deposit substantivo | /dɪˈpɑ.zɪt/ | depósito |
Phrasal verbs que você vai ouvir
| Palavra | Pronúncia | Significado |
|---|---|---|
| set up verbo | /ˌsɛt ˈʌp/ | preparar |
| check out verbo | verificar, sacar só |
Pronúncia para ficar de olho
O falante usa 12 contrações e formas reduzidas, como we've, we're, don't. Diga-as na forma curta, do jeito que você ouve.
- Os sons de “sh” e “zh”: insufficient /ɪnsəˈfɪʃənt/, inspection /ɪnˈspɛkʃən/, contamination /kənˌtæm.əˈneɪ.ʃən/, flash /flæʃ/, sheet /ʃit/
- Palavras longas — acerte a sílaba tônica: insufficient /ɪnsəˈfɪʃənt/, contamination /kənˌtæm.əˈneɪ.ʃən/, automatic /ˌɔː.təˈmæt.ɪk/, manufacturer /ˌmænjʊˈfæktʃəɹə/, dimensional /daɪˈmɛn.ʃə.nəl/
Como praticar com este vídeo
- Ouça o vídeo inteiro uma vez sem falar e anote as palavras que você não conhece.
- Faça shadowing frase por frase na velocidade normal, repetindo cada uma até o seu ritmo ficar igual ao do falante.
- Grave a sua voz e compare com o original, prestando atenção a palavras como flux, pasta, component.
O que é a Técnica de Shadowing?
Shadowing é uma técnica de aprendizado de idiomas com base científica, originalmente desenvolvida para o treinamento de intérpretes profissionais. O método é simples, mas poderoso: você ouve áudio em inglês nativo e repete imediatamente em voz alta — como uma sombra seguindo o falante com 1-2 segundos de atraso. Pesquisas mostram melhora significativa na precisão da pronúncia, entonação, ritmo, sons conectados, compreensão auditiva e fluência na fala.