Bob
=======================
Robert
Barr
Manufacturing Engineering
Formation, Inc.
Voice: 856-234-5020
x3035
Fax: 856-234-6679
-----Original Message-----
From: Becerra Alejandro [mailto:[log in to unmask]]
Sent: Wednesday, May 29, 2002 1:41 PM
To: 'TechNet E-Mail Forum.'; 'bbarr'
Subject: RE: [TN] FPBGA Area Ratio QuestionBob,
I calculate the area ratio using a 5 mil stencil and my numbers do not agree with yours.1. Square aperture of 0.013". Area of Aperture = 0.000169.
Area of Lateral Walls = 0.013 X 4 X 0.005 = 0.00026.
Area Ratio = 0.000169/0.00026 = 0.65.2. Square aperture of 0.012". Area of Aperture = 0.000144.
Area of Lateral Walls = 0.012 X 4 X 0.005 = 0.00024.
Area Ratio = 0.000144/0.00024 = 0.60.If you take into account the radiused corners the area ratio may be lower.
I calculate for the option 1 (with radiused corner of 0.003") and it was 0.68.
When you reduce the size of the apertures with the same stencil thickness the area ratio is reduced (not increased)Regards,
Alejandro Becerra
-----Original Message-----
From: bbarr [mailto:[log in to unmask]]
Sent: Wednesday, May 29, 2002 9:40 AM
To: [log in to unmask]
Subject: [TN] FPBGA Area Ratio Question
On a fine pitch BGA (.8mm pitch, 384 balls, .5mm ball diameter) I am using a
.014" diameter land per TI's recommendation. I was thinking then of a .013"
square stencil aperture with .003" radiused corners on a 5 mil plate. This
seemed reasonable until I did an area ratio calculation per IPC-7525. The
result was .592, which fails compared to the acceptable value of >.66. The
aspect ratio is a solid 2.6, although IPC says I should not consider aspect
ratio in this case, only area ratio. If I reduce down to a .012" square
aperture I can get to an area ratio of .642. Still fails, but close. But,
reducing the aperture 2 mils compared to the pad seems extreme and violates
the recommendation in para. 3.2.2.4. So my question is, what do you guys and
gals use for an aperture design on a component like this? Do you go by the
IPC guidelines?Thanks.
Bob
=======================
Robert Barr
Manufacturing Engineering
Formation, Inc.
Voice: 856-234-5020 x3035
Fax: 856-234-6679---------------------------------------------------------------------------------
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