Shadowing-Übung: Understanding BGA Pads: Solder Mask Defined vs Non-Defined - Englisch Sprechen Lernen mit Video

Hello everyone, welcome back to Altium Academy.

I'm your host Zach Peterson and today we're going to be talking about BGA pads

and specifically solder mask defined pads and non -solder mask defined pads.

Now we got a great viewer question about this topic as it relates to IPC density levels in the IPC 7351 standard.

We're going to go over all of that data today

and I'll tell you how much you can expand your pad

sizes in order to create solder mask defined pads for your BGA it.

Let's jump in and get started.

So for this video, we got a question on one of our older BGA pad size videos.

Let's take a look at that viewer question.

Vicky Khan 6309 writes, Zach, what is the meaning of land pattern density level?

I have read PCB pad to component pads should be in the ratio of 1 to 0 .8.

How can we decide whether to use SMD or NSMD BGA pads?

Vicky, this is a great question and I actually see a few questions here,

all of them relating to how we design BGA footprints to be compliant with the IPC 7351 standard and how we

defined pads for a component.

Let's take a look at some of the standard pad size allowances under the 7351 standard, how they relate to ball diameter,

and how those relate to IPC density levels.

So to answer all of these questions, first we have to look at what is the IPC 7351 standard.

So here I'm on the Altium blog.

I have an article up here about the IPC 7351 standard and how to

of some of the information you get from the 7351 standard.

There are these formulas that you can use to calculate the size of the copper pads

that will go on your PCB to accommodate different types of components.

Now of course this just relates to a specific SMD package.

What about BGAs?

Well here we have another article on the Ultium blog specifically about BGA pads

and here you can see on screen we have the BGA pad size video where this question was posted.

So here when land pattern, we have some allowed range of pad sizes that we can use,

and that pad size is a function of the ball diameter on the bottom side of the BGA package.

So the ball diameter you can find from the component data sheet, and if you look through the component data sheet in the mechanical drawing,

you will see a measure of the ball size on the bottom side of that package.

Here in this table, we have ball diameters listed in the left column, and then there's a density response to.

So these density levels are the IPC 7351 density levels that were referenced in the question.

So density level A is something that is intended for low density placement and assembly.

Basically, you could probably place and solder components with IPC density level A footprints by hand.

Once you go to density level B, you can probably place them by hand, but you'll probably need automated assembly and a reflow oven.

Once you get the density level C, the density is going high that you're going to need automated placement and automated soldering in a reflow oven.

Now you can see here in this table within those three density levels, we have broken out our possible range of pad sizes for a BGA.

Here you can see, for example, the land variation at the largest ball diameter of 0 .75 millimeters.

We have a land variation of 0 .5 to 0 .6 millimeters.

And of course, this continues to reduce the smaller

and smaller land size variation as we get to smaller and smaller balls on the bottom side of the BGA package, just as we might expect.

Now, we need to have a pretty big asterisk on this table

because this table only applies for packages where the balls on the bottom side of the BGA collapse during soldering.

We also have non -collapsing balls on some packages.

What I did is I did a little bit of research and I found on the PCB Libraries forum,

there is a corresponding table here for non -collapsing balls on BGA packages.

And you can see what the pad variation is for these packages.

at the 0 .75 millimeter ball diameter we actually have much

larger possible pad variation from 0 .81 millimeters to 0 .91

millimeters you have to have a larger allowance on the pad size

when you have a non -collapsing ball on your bga package

now let's get into the next part of the question what about using smd

or non -smd pads well to determine what range of possible negative solder mask expansion

compiled all of this data into a table as you can see here in Excel.

From looking at the land size from largest to smallest we

can then determine how large our negative mask expansion can be

in order to form a non -solder mask versus solder mask defined pad and still comply with the IPC 7351 standards.

So let's take a look at the first entry in this table.

Here in this table you can see

that we can have a land size variation from 0 .5 millimeters to 0 .6 millimeters.

One option to

pad from a non -soldermask defined pad is to place a 0 .6 millimeter pad

and then apply a negative 0 .1 millimeter expansion and

that will bring it down to a 0 .5 millimeter exposed copper pad for your BGA.

So that would still comply with the IPC 7351 standards because the size of your exposed land is still 0 .5 millimeters.

And you can continue this example all the way down the table to these really small ball diameters

when you're at density level C.

Here in the lower half of this chart, I've converted all of these values to mils for those of you who like to use the Imperial system.

Here you can see that we have a land size variation from 23 .6 to 19 .685.

to the largest pad size, That would expose enough copper corresponding to the smallest land size,

and you'll still comply with IPC 7351 standards for density level A.

Now that we know the variation we can apply in our copper pads and still comply with the IPC 7351 standards, let's take a look at an example in Altium Designer.

So here on screen, I have an Ethernet switch project.

I've been talking it up a little bit recently, and it's in the process of getting assembled.

But you can see it here on screen in 3D.

Now, if we go into 2D, let's just take a look at this central component.

This is our Ethernet controller.

You can see here that we have some pads available.

just click on one of these pads

and look over in the properties panel we can see that our pad size is 0 .5 millimeters.

Now if we go over to the data sheet

and look at the mechanical drawing we can see here what the ball size is.

In the side view you can see

that we have a dimension for the outer diameter of the solder ball on the bottom of the package

and you can see down here in this table that the nominal ball size is 0 .6 millimeters.

Going back over to our table from the IPC 7351 standard for this component we see

that we could have a land variation of 0 .4 to 0 .5 millimeters

and that will comply with IPC 7351 density level A.

Now let's jump back into Altium Designer.

So let's take a look at what's going on with the solder mask expansion in this pad.

Here you can see that we have rule expansion set, so we need to look in the design rules.

And if we just look under the solder mask expansion rule, you can see that this is the only rule we have that applies to pads, and the expansion is .064 millimeters.

So we actually have positive expansion here, so this is a non -solder mask defined pad.

If we wanted to reduce the exposed pad area, we could apply a negative mask expansion here.

Or we could even expand the copper a bit more so

that we still leave that 0 .5 millimeter pad exposed through the solder mask opening.

Now what's the fastest way to do that?

100

Well, this is a 676 pin component.

101

I don't want to go through and manually select 676 pins and edit the solder mask.

102

So the fastest way to do this is to use a design rule query

103

and set a new expansion value that only applies to this BGA.

104

So how can we do that?

105

Well, we can use the new rule option and we can create a custom query.

106

And there's a couple of queries that we could use to do this.

107

We could use the HAVS footprint query and then select the footprint for this BGA.

108

The other thing that we could do is we could create a room around

109

that BGA and we could use the within room query

110

Either of those is going to allow us to set a solder mask expansion value

111

that only applies to the pads for that component and it won't affect anything else in the design.

112

This is a good way to control whether you have solder mask defined pads

113

or non solder mask defined pads while still complying with the IPC7351 standards for your density level.

114

Now suppose we wanted to expand the size of these pads.

115

How big can we expand them?

116

Well, that's going to be limited by our etching clearance, and it's especially going to be limited if we need to route a trace in between any of these pads.

117

Let's take a look down here near the edge.

118

You can see that for one of these Ethernet lanes, I have one of the traces routing in between two pads,

119

and that trace has a set width that's based on the target impedance for this Ethernet interface.

120

Of course, if the pads get too large, the clearance between the pad and the nearby trace will get too small,

121

and we won't be able that is one way to set the limit between the pad size and any nearby object,

122

whether it's another pad or another trace.

123

When you set your etch clearance limits, those rules should take priority over any kind of solder mask expansion

124

or negative mask expansion that you're using to create your SMD pads.

125

Always make sure you're obeying that etch clearance limit when you're creating your footprints, or if you're manually modifying your pad sizes to apply that expansion to create SMD pads.

126

Thanks for sending in this great question.

127

We don't get a lot of footprint questions, but when we get a good one, I'm always happy to answer it.

128

So if you're watching right now, make sure to leave your comments and questions in the comment section.

129

Make sure to hit that subscribe button.

130

You'll be able to keep up with all of our tutorials as they come out.

131

And last but not least, don't forget to call your fabricator, folks.

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Shadowing ist eine wissenschaftlich fundierte Sprachlerntechnik, die ursprünglich für die professionelle Dolmetscherausbildung entwickelt und durch den Polyglotten Dr. Alexander Arguelles populär gemacht wurde. Die Methode ist einfach aber wirkungsvoll: Du hörst englisches Audio von Muttersprachlern und wiederholst es sofort laut — wie ein Schatten, der dem Sprecher mit nur 1–2 Sekunden Verzögerung folgt. Anders als passives Hören oder Grammatikübungen zwingt Shadowing dein Gehirn und deine Mundmuskulatur, gleichzeitig echte Sprachmuster zu verarbeiten und zu reproduzieren. Studien zeigen, dass es Aussprachegenauigkeit, Intonation, Rhythmus, verbundene Sprache, Hörverständnis und Sprechflüssigkeit signifikant verbessert — was es zu einer der effektivsten Methoden für die IELTS Speaking-Vorbereitung und reale englische Kommunikation macht.

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