IPC-SM-782A 表面安装设计和焊盘设计标准(带BGA).pdf - 第67页
Land Pattern Details The information in the following sections is intended to represent requirements for families of surface-mountable compo- nents that have been standardized by standard developers throughout the world …
There are various tools available for removing components.
Resistance heating tweezers are also used for removing
surface mounted components. Various types of hot air/gas
and IR systems are also used for removing surface
mounted components. One of the main issues when using
hot air/gas devices is preventing damage to adjacent com-
ponents.
No matter which system tool is used, all the controlling
desoldering/soldering variables, such as number of times a
component can be removed and replaced, desoldering tem-
perature and time, and damage to the packaging/
interconnection assembly, need to be addressed.
IPC-SM-782A December 1999
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Land Pattern Details
The information in the following sections is intended to represent requirements for families of surface-mountable compo-
nents that have been standardized by standard developers throughout the world (e.g., EIA, JEDEC, and EIAJ). The prin-
ciples used in the data embody the concepts of ‘‘design for manufacturability,’’ and specify criteria for analysis or modifi-
cation in order to make the manufacturing process as robust as possible.
Each component family type has been organized into a four-page set that has its own number identification (a paragraph
number of the mother document—IPC-SM-782) and its own revision status. As changes are necessary (the addition or dele-
tion of information, or corrections to modify the text or numerical data), a four-page signature(s) will be reissued as a set
for replacement in this handbook.
A summary of the contents with revision status is provided at the conclusion of this explanation.
Introduction
Page 1 of each data set (four-page signature) provides general information about the part, its usage or performance require-
ments, and techniques for handling the attachment of the component. Any useful information about the particular compo-
nent type is detailed on this introductory page.
Component Dimensions
Page 2 of each data set describes the critical component dimensions necessary to make judgements for reliable mounting
recommendations. The standards organizations provide many more dimensions to define the requirements for manufacturing
the specific components in a family class; only those dimension that are necessary for land pattern development are repeated
on page 2 of each data set.
Every attempt has been made to check and correlate the dimensions used against the published standard. Unfortunately, the
standards do not always provide adequate information, or full disclosures of maximum and least material conditions of the
component dimensions used in land pattern development. At times, the numbers shown in the data set have been enhanced
(nominal dimensions converted to maximum/minimum dimensions), at times the numbers shown have been derived (termi-
nal dimensions subtracted from an overall dimension with their inherent tolerances considered in an RMS condition), and
at other times the dimensions have been tailored (total tolerances spread between maximum/minimum limits reduced to a
reasonable amount) in order to facilitate a producible land pattern and assembly.
Users are encouraged to check with their component suppliers in order to ascertain that the suppliers certify to the numbers
used on page 2 in order to use the registered land patterns on page 3. In the event of disparities, if they are component-
supplier specific, users are encouraged to modify their use of the land patterns shown on page 3 in accordance with the prin-
ciples outlined in Section 3.3 on the registered land patterns dimensioning system. If the disparities are industry specific,
please inform the IPC using the form at the end of this section to initiate a data set change.
Land Pattern Dimensions
Page 3 of the data set provides the details for the land pattern. Since the design concepts are dedicated to establishing the
most favorable solder joint conditions, all land pattern dimensions are shown at maximum material condition (MMC). This
is the ‘‘target value’’ for the board manufacturer; moving away from MMC to the least material condition (LMC) reduces
the opportunity for formation of the optimum solder fillet. The LMC dimensions should not exceed the fabrication (F)
allowance shown on page 4. The LMC and the MMC provide the limits for each dimension.
In addition to specifying maximum and minimum limits, the resultant land width is provided as a reference (dimension
‘‘Y’’). Designers are encouraged to incorporate the MMC conditions into their library symbols, and when sending electronic
data to their board manufacturer they should identify that the data is at MMC. Specifying minimum conductor width as a
manufacturing goal should be avoided, since the manufacturer is compensating and scaling data to accommodate process
allowances in the phototool, and is concentrating on meeting minimum requirements. This is opposite to the desire to have
robust land patterns which should be at maximum material conditions.
Page 3 also provides an area around the land pattern known as the ‘‘grid courtyard.’’ The description is in the 0.05 mm ele-
ments of the international grid. An area described as 4x6 is equal to 2.00 mm by 3.00 mm. When placing parts on a printed
board, the highest density is when one courtyard touches another. Courtyards are intended to encompass the land pattern
and a component body that is centered on the land pattern.
December 1999 IPC-SM-782A
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Tolerance Analysis
Page 4 shows the details of the tolerance analysis of the component and land pattern shown in the data set. The first two
columns of the table show the board fabrication allowances in the analysis; the second column shows the allowances used
to represent placement registration in terms of DTP (diameter of true position), with the point of origin being the center of
the land pattern.
The next part of the analysis provides three pieces of information for the toe fillet, heel fillet, and side fillet. The first part
of the set is the range of differences between maximum and minimum component dimensions. These are: the overall dimen-
sion (usually ‘‘L’’) identified as ‘‘C’’; the inside dimension l (usually ‘‘S’’) identified as ‘‘C’’; and the side or lead width s
(usually ‘‘W’’) identified as ‘‘C.’’ The second and third columns w of each triplet set show the minimum and maximum sta-
tistically derived solder fillet opportunity. These two columns become the upper and lower specification limits for any sta-
tistical process control (SPC) analysis. If these conditions are not met, something has shifted in the process, or the parts
being assembled in the process.
Revision Status
The following is the revision status of the component family data sets of IPC-SM-782A. A dash (‘‘-‘‘) signifies that the sec-
tion is the original release; the letter ‘‘A’’ after the section number refers to the first revision to the four-page set; the letter
‘‘B’’ refers to the second revision, etc.
Section Revision
Number Status Section Title
8.0 — Discrete Components
8.1 A Chip Resistors
8.2 A Chip Capacitors
8.3 — Inductors
8.4 A Tantalum Capacitors
8.5 A Metal Electrode Face (MELF) Components
8.6 — Small Outline Transistor (SOT) 23
8.7 — Small Outline Transistor (SOT) 89
8.8 A Small Outline Diode (SOD) 123
8.9 — Small Outline Transistor (SOT) 143
8.10 — Small Outline Transistor (SOT) 223
8.11 A Modified Through-Hole Component (TO) 252
9.0 — Components with Gullwing Leads on Two Sides—
9.1 A Small Outline Integrated Circuits (SOIC)
9.2 A Small Outline Integrated Circuits (SSOIC)
9.3 A Small Outline Package Integrated Circuit (SOPIC)
9.4 A Thin Small Outline Package
9.5 — Ceramic Flat Pack (CFP)
10.0 — Components with J Leads on Two Sides
10.1 A Small Outline Integrated Circuits with J Leads (SOJ)—7.63 mm [0.300] Body Size
10.2 — Small Outline Integrated Circuits with J Leads (SOJ)—8.88 mm [0.350] Body Size
10.3 — Small Outline Integrated Circuits with J Leads (SOJ)—10.12 mm [0.400] Body Size
10.4 — Small Outline Integrated Circuits with J Leads (SOJ)—11.38 mm [0.450] Body Size
11.0 — Components with Gullwing Leads on Four Sides
11.1 A Plastic Quad Flat Pack (PQFP)
11.2 A Shrink Quad Flat Pack (SQFP), Square
11.3 A Shrink Quad Flat Pack (SQFP), Rectangular
11.4 A Ceramic Quad Flat Pack (CQFP)
12.0 — Components with J Leads on Four Sides
12.1 A Plastic Leaded Chip Carrier (PLCC), Square
12.2 A Plastic Leaded Chip Carrier (PLCC), Rectangular
12.3 — Leadless Ceramic Chip Carrier (LCC)
13.0 — Modified Dual-In-Line Pin (DIP) Components
13.1 — DIP
14.0 – Components with Ball Grid Array Contacts
14.1 – Plastic Ball Grid Array
14.2 – 1.27 mm Pitch Rectangular PBGA JEDEC MS-028
IPC-SM-782A December 1999
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