What is SMT?(十五) -- Failure reduction methods
author: Hellen
2022-10-14
The manufacturing process, handling, and printed circuit assembly (PCA) testing all put the package under a lot of mechanical stress, which can lead to failure. As grid array packages become larger and larger, it becomes more difficult to set the level of safety for these steps.
For many years, a typical feature of packages has been the use of the monotonic bend point test method, described in IPC/JEDEC-9702, "Monotonic Bend Characteristics of Board Level Interconnects". This test method describes the fracture strength of the horizontal interconnection of printed circuit boards under bending loads. However, the test method cannot determine what the maximum allowable tension is.
One of the challenges for the manufacturing process and assembly process, especially for lead-free PCA, is the inability to directly measure the stress on the solder joints. The most widely used metric to describe the risk of interconnected components is the printed circuit board tension adjacent to the component, as described in IPC/JEDEC-9704, Guide to Strain Testing of Printed Wiring Boards.
As the use of lead-free devices expands, so does the interest of users; as there are many users facing quality issues.
With this increased interest from all parties, IPC felt the need to help other companies develop various test methods that would ensure that BGAs were not damaged during manufacturing and testing. This work was done by the IPC 6-10d SMT Attachment Reliability Test Methodology Working Group and the JEDEC JC-14.1 Packaging Device Reliability Test Methodology Sub-Committee, and the work is now complete.
The test method specifies eight contact points arranged in a circular array. The PCA with a BGA in the center of the printed circuit board is placed so that the part is mounted face down on the support pins and the load is applied to the back of the BGA. The strain gage is placed adjacent to the part according to the recommended metering layout of IPC/JEDEC-9704.
The PCA will be flexed to the relevant tension levels and failure analysis will determine the extent of damage caused by flexing to these tension levels. An iterative method is used to determine the tension level at which no damage occurs, which is the tension limit.
For many years, a typical feature of packages has been the use of the monotonic bend point test method, described in IPC/JEDEC-9702, "Monotonic Bend Characteristics of Board Level Interconnects". This test method describes the fracture strength of the horizontal interconnection of printed circuit boards under bending loads. However, the test method cannot determine what the maximum allowable tension is.
One of the challenges for the manufacturing process and assembly process, especially for lead-free PCA, is the inability to directly measure the stress on the solder joints. The most widely used metric to describe the risk of interconnected components is the printed circuit board tension adjacent to the component, as described in IPC/JEDEC-9704, Guide to Strain Testing of Printed Wiring Boards.
As the use of lead-free devices expands, so does the interest of users; as there are many users facing quality issues.
With this increased interest from all parties, IPC felt the need to help other companies develop various test methods that would ensure that BGAs were not damaged during manufacturing and testing. This work was done by the IPC 6-10d SMT Attachment Reliability Test Methodology Working Group and the JEDEC JC-14.1 Packaging Device Reliability Test Methodology Sub-Committee, and the work is now complete.
The test method specifies eight contact points arranged in a circular array. The PCA with a BGA in the center of the printed circuit board is placed so that the part is mounted face down on the support pins and the load is applied to the back of the BGA. The strain gage is placed adjacent to the part according to the recommended metering layout of IPC/JEDEC-9704.
The PCA will be flexed to the relevant tension levels and failure analysis will determine the extent of damage caused by flexing to these tension levels. An iterative method is used to determine the tension level at which no damage occurs, which is the tension limit.
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