Luyện nói tiếng Anh bằng Shadowing qua video: PCB Inspection Methods & Common PCB Defects
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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.
Về Bài Học Này
Bạn đang luyện tập phát âm tiếng Anh với video "PCB Inspection Methods & Common PCB Defects" bằng phương pháp Shadowing — kỹ thuật được Dr. Alexander Arguelles phổ biến rộng rãi.
Hãy nghe kỹ từng câu, chú ý cách người nói nhấn âm và nối âm, rồi đọc lại to và tự tin. Mỗi ngày 15–30 phút luyện đều đặn, bạn sẽ thấy phát âm chuẩn hơn.
Phương Pháp Shadowing Là Gì?
Shadowing là kỹ thuật học ngôn ngữ có cơ sở khoa học, ban đầu được phát triển cho chương trình đào tạo phiên dịch viên chuyên nghiệp và được phổ biến rộng rãi bởi nhà đa ngôn ngữ học Dr. Alexander Arguelles. Nguyên lý cốt lõi đơn giản nhưng cực kỳ hiệu quả: bạn nghe tiếng Anh của người bản xứ và lặp lại to ngay lập tức — như một "cái bóng" (shadow) đuổi theo người nói với độ trễ chỉ 1–2 giây. Khác với luyện ngữ pháp hay học từ vựng bị động, Shadowing buộc não bộ và cơ miệng phải đồng thời xử lý và tái tạo ngôn ngữ thực tế. Các nghiên cứu khoa học xác nhận phương pháp này cải thiện đáng kể phát âm, ngữ điệu, nhịp điệu, nối âm, kỹ năng nghe và độ lưu loát khi nói — đặc biệt hiệu quả cho người luyện IELTS Speaking và muốn giao tiếp tiếng Anh tự nhiên như người bản ngữ.