4
\$\begingroup\$

I want to create a footprint for a BGA-292 package. I might be wrong but there are 2 different views of the package in the datasheet. The first outline shows:

enter image description here

In the photo above, the right side should be the flipped view of the top-view on right side. This makes sense, but, there is a top-view view of the pins as well:

enter image description here

If you look carefully, this does not match the first picture. Rows and columns are swapped while the A1 pin is still on the bottom-right corner of both pictures. Which one should I trust?

What does the TOP-VIEW mean? is it looking through the top of the package into pins? then why numerical and alphabetical columns and rows are swapped?

\$\endgroup\$
  • \$\begingroup\$ What make and part number is the part in question? \$\endgroup\$ – ThreePhaseEel Aug 6 '17 at 15:25
6
\$\begingroup\$

Draftspeople at 90° angles

The draftsperson who drew the pin map drawing drew it rotated 90° from the draftsperson who drew the package drawing. Rotating it 90° clockwise makes the index pin (A1) match up with the location of the index mark on the top view in the package drawing, as seen below:

pin map, rotated 90° clockwise

The top view part, by the way, means exactly what you think it does -- you're looking through the top of the package into the pins with a metaphorical X-ray camera. This means that it matches how you'd map the pins to your PCB footprint.

\$\endgroup\$
  • \$\begingroup\$ Then flip left-to-right to match the top-view diagram with the bottom-view diagram labels on the right. \$\endgroup\$ – Tom Carpenter Aug 6 '17 at 15:47
  • \$\begingroup\$ @TomCarpenter -- yeah, the top view vs bottom view thing is a lot more common than the rotation thing though \$\endgroup\$ – ThreePhaseEel Aug 6 '17 at 15:49
6
\$\begingroup\$

You will find that both diagrams actually have exactly the same pin mapping, though it is slightly obfuscated. The first thing we have to do is identify which side is which in the diagrams. In the top diagram we have:

Datasheet Diagram Labelled with Top/Bottom View

On the left we have the top view, which indicates looking down on the top of the chip. On the right we have the bottom view, looking up at the bottom (pin side) of the chip.

From this we see that the diagram with labelling of the pins is from bottom view. That means that it is the mirror image of how the pins would appear on the footprint/PCB pins.

In your second diagram you have the pin-out for the chip laid out as a Top-View image (as labelled) and so matches how the pins would appear on the PCB. As such in order to directly compare the two diagrams, we must flip one or other of them in order to get them to be viewed from the same side. Lets make both Top-View by flipping the package drawing:

Package Drawing Flipped to Top-View

Pin Map Labelled

You can see now that pin-out in the package diagram does match the pin map diagram, with only a rotation as noted in the other answers.

\$\endgroup\$
  • \$\begingroup\$ Thanks for detailed answer and effort on flipping the image. \$\endgroup\$ – Sean87 Aug 6 '17 at 16:48
3
\$\begingroup\$

Rotate it by 90 degrees, then it will match up.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for?Browse other questions tagged or ask your own question.