शैडोइंग अभ्यास: PCB Inspection Methods & Common PCB Defects - वीडियो के साथ अंग्रेजी बोलना सीखें

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140 वाक्य

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This is the next video in the PCB series.

Here we're going to be looking at printed circuit board assemblies and the inspection methods and common defects.

So checking solder paste process.

There are a number of points to check for with the solder paste process.

1. We need to be looking at the paste stencil alignment.

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,

alignment dots on the PCB.

We covered this in a previous video.

The manual method of setting up the stencil is to align the stencil with the PCB printed pads.

then set the clamp stops to hold the PCB in the correct place.

What to check for?

Well you need to check the solder paste is correctly aligned to all of the pads on the PCB.

Over on the right here we can see three images.

The top image, which is good, shows that all of the paste is aligned with the pads.

The middle shows some errors we can see here, slight misalignment and one bridge between two solder plates.

The bottom one is just a mess, i.e. the ugly looking thing, with solder all over the place.

Two, the squeegee speed and pressure.

The squeegee speed should not be too fast that the paste does not roll as it moves across the stencil

or too slow

that the print cycle time does not keep up with the manufacturing line The blade pressure is usually set

so that no paste remains on the stencil behind the squeegee

Higher pressures will not only damage the stencil but also shear thin the paste

to such an extent that the flux will separate from the metal and problems such as paste sticking to the blade,

lack of tack at placement or poor solderability will occur further down the assembly line.

What to check for?

We need to check for solder paste is not left on the stencil after a pass

and that all the solder pads have adequate paste deposited.

Again on the right hand side here, going from the top left, 1, the alignment gasket of apertures to the pad.

2, we need to check the squeegee motion, things paste so it flows into the apertures.

3, bottom left, paste, recovers, stiffens up.

And of 4, the bottom right, the stencil separates from PWB, paste deposits release from the stencil into the pads.

Now let's have a look at the five major issues with pick and place machines.

Fault number one, loss of vacuum.

What to check for?

Or primary process set up areas to check.

Is nozzle damaged and will not sit flush against the component's surface?

Or damaged vacuum hoses or a vacuum system?

Fault number two, short or worn nozzles.

What to check for?

Short nozzles will result in components not being placed correctly resulting in component shift and movement.

Worn nozzle tips result in loss of vacuum and you will see components being dropped.

Measure nozzles against dimensional acceptance.

Thought number 3.

Sticking nozzles.

What to check for?

Damaged nozzles that do not fit correctly into their holders.

old and non-maintained nozzles.

On the right hand side there you can see the top image showing the nozzle area.

Make sure these are not worn or damaged in any way.

The bottom image just shows a variety of different nozzles that can be used.

Thought number four, higher than normal reject rates at inspection.

What to check for components were not presented to the nozzle in a consistent position,

poor nozzle alightening from degradation of reflective discs or nozzle face over time,

dirty reflective discs or nozzle face, a poor quality of reflective disc or nozzle face,

nozzle height is incorrect, And finally, stuck nozzles from part height incorrect setting program.

Nozzle worn beyond their tolerances or incorrect length tolerance on nozzles.

Fault number 5.

Component and circuit board damaged caused by ESD.

What to check for?

Ensure nozzles are manufactured from electrostatic dissipating materials.

manufacturing manufacturers data sheet for this.

What to check for with incorrect wave solder profile.

Default here is bridging.

What to check for?

Well the primary process setup areas to check are conveyor speed too slow or other incorrect solder wave settings,

time Overheat is too long causing flux to be burnt off.

Dwell time is too long causing the flux to burn off before exiting the wave.

Top side board temperature too low.

Not enough flux applied to the flux activity is too low.

You can see here in this image solder bridging between two points.

the incorrect wave soldering profile issue, the fault being insufficient solder on topside fillet.

What to check for?

Conveyor speed is too low.

Check the time over preheat too long, causing the flux to be burned off.

Dwell time is too long, causing flux to be destroyed before exiting the wave.

The conveyor speed is too fast.

Dwell time is too short.

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,

solder temperature too low it cools in the barrel before it reaches the topside,

and wave height too low in one or both waves so the solder does not contact the board properly.

In this image it clearly shows there is insufficient solder to make this a good contact.

Another incorrect wave solder profile issue

so the fault here is insufficient solder bottom side fillet conveyor

speed is too slow time over preheat too long causing the

flux to be burnt off dwell time is too long causing flux to be destroyed before it exits the wave.

Bottom side board temperature is too high causing flux to be burnt off before the wave

and not enough flux or flux activity.

The wave height is too low on one or both waves.

And we can see here on the right hand side we've got problems with that connector.

On the bottom is insufficient solder where this component is placed.

Another incorrect wave solder profile issue, the fault here, is de-wetting or non-wetting.

What to check for?

Usually the board related due to contamination on the surface of the pads.

Solder temperature too low, solder wave height too low, contaminated flux or contaminated solder.

Or the conveyor speed is too high or too low.

And again, we can see examples here of solder de-wetting or non-wetting in the bottom instance.

Another incorrect wave solder profile issue is solder voids.

Now what to check for here.

Topside or overall board temperature is too low in trapping moisture that is outgassed at the wave.

100

Entrapped fluid by component in through hole.

101

Chemical contaminants not removed during PC fabrication process.

102

Contamination in the hole.

103

Top side of the hole covered by component body or flashing.

104

You can see an example of a solder void here.

105

Another fault is solder skip.

106

Now what to check for?

107

Conveyor speeds too fast.

108

so the dwell was too short in the wave.

109

Make sure the chip or turbine wave is turned on.

110

Not enough flux for the solder to bond.

111

Wave height too low on one or both waves.

112

You can clearly see here this pad has no solder at all.

113

Another fault is icicles or flags or horns.

114

Now what to check for?

115

conveyor speeds too slow.

116

Time over preheat too long causing flux to burn off.

117

Dwell time too long causing flux to be destroyed before exiting to the wave.

118

Solar temperature too low, not enough flux.

119

The use of nitrogen will help prevent icicles.

120

You can see a good example here of what we're talking about when we mention solar flags.

121

Another fault is solder on mask Poor flux application Flux and resist incompatibility Poor cure of the solder mask

122

Preheat temperatures too high Solder temperature too high This image just shows the solder on the mask itself

123

another fault is rough or disturbed solder check conveyor for vibration or jerky motion

124

removal of the board prior to the solder solidifying solder temperature too low conveyor speed too high and wave run uneven

125

you can see what we're talking about with rough solder in this image

126

just to summarize here's an image of some common faults I'm

127

just going to go through these with the top left moving to the right

128

so we've got lifted component we've got tombstone effect

129

wrong polarity upside down mounting in the second row we have a missing component

130

we have that missing solder that we saw earlier we have a lifted lead

131

we've got that solder bridging again

132

on the bottom row we've got billboarding then we have shifted or twisted component we have our solder flags again

133

and that solder void

134

don't forget to check out our other videos in this PCB series

135

and you can contact us if you need any help with your projects at all in China.

136

Don't forget to like, share and subscribe to our channel.

137

And you see there's a little bell symbol.

138

If you hit that, you'll get a notification every time we upload new content.

139

Thanks for listening.

140

My name is Paul Adams from South East 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 140 वाक्य और 1559 शब्द हैं। बोला गया हिस्सा 12:27 लंबा है। वक्ता लगभग 125 शब्द प्रति मिनट की स्थिर गति से बोलता है, जो शैडोइंग के लिए आरामदायक है। केवल 76% 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
pasta संज्ञा	/ˈpɑ.stə/	पास्ता
incorrect विशेषण	/ˌɪn.kəˈɹɛkt/	त्रुटिपूर्ण
exit संज्ञा	/ˈɛɡzət/	प्रस्थान, निकासी
vacuum संज्ञा	/ˈvæ.kjuːm/	निर्वात
mask संज्ञा	/mæsk/	मुखौटा, मास्क
void विशेषण	/vɔɪd/	रिक्त
reflective विशेषण	/ɹɪˈflɛktɪv/	परावर्ती
deposit संज्ञा	/dɪˈpɑ.zɪt/	भंडार
blade संज्ञा	/bleɪd/	ब्लेड
inspection संज्ञा	/ɪnˈspɛkʃən/	निरीक्षण, जाँच
contamination संज्ञा	/kənˌtæm.əˈneɪ.ʃən/	मिलावट
extent संज्ञा	/ɪkˈstɛnt/	विस्तार
mount क्रिया	/maʊnt/	चढ़ना
occur क्रिया	/əˈkɜː/	बीतना
thin विशेषण	/ˈθɪn/	पतला, दुबला

ध्यान देने योग्य उच्चारण

वक्ता 12 बार संक्षिप्त रूपों का प्रयोग करता है, जैसे we've, we're, don't। इन्हें वैसे ही छोटा बोलें जैसा आप सुनते हैं।

“sh” और “zh” की ध्वनियाँ: insufficient /ɪnsəˈfɪʃənt/, inspection /ɪnˈspɛkʃən/, contamination /kənˌtæm.əˈneɪ.ʃən/, flash /flæʃ/, sheet /ʃit/
लंबे शब्द — बलाघात सही रखें: insufficient /ɪnsəˈfɪʃənt/, contamination /kənˌtæm.əˈneɪ.ʃən/, automatic /ˌɔː.təˈmæt.ɪk/, manufacturer /ˌmænjʊˈfæktʃəɹə/, dimensional /daɪˈmɛn.ʃə.nəl/

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 pasta, incorrect, exit 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।

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इस वीडियो से अभ्यास कैसे करें

शैडोइंग तकनीक क्या है?