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Ipc 9704 pdf download. PCB Strain Measurement
Ipc 9704 pdf download. Ipc Jedec9704a
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There may be unique manufacturing processes that require alternative configurations. For example, through-hole components typically require wave solder. Wave solder conventionally follows convection reflow one or two passes depending on board layout. In cases where assembly characterization prior to wave solder is required, the test board shall be mechanically representative of boards prior to SMT reflow.
In such instances, alternative set-ups are acceptable as long as all mechanical loading characterization requirements are met. It is recommended that test boards be inspected for excessive warpage prior to instrumentation.
Another possible consider- ation would be the effect of solder aging, i. This should be considered when interpreting the results. If there are several fine pitch components, then, at a minimum, the three worst case locations should be tested based on engineer- ing judgment, history of damage, or finite element analysis. The above represents one of the methods that may be employed as a criterion for characterization.
Printed board and package design considerations include geometry, materials, and configuration. For printed boards with a large number of BGA components i. However, if initial testing identifies areas of high strain, this should be followed up with more comprehensive testing in the area of concern.
CAUTION: Where such methods are employed, it is important to recognize that one may not fully understand all the loads that will be applied, to all locations, at all loading operations. In all cases, it is recommended that the four package corners be strain gaged unless space constraints make this impossible. Differences between socket designs make con- sistent strain gage placement impractical.
In general, strain gages will be placed between 6 mm and 10 mm from the BGA corner solder joints. Strain gages should only be placed at customer or vendor specified locations and orientations when measurements are being directly compared to customer or vendor specified strain guidance. See the www. Selection of components on which to place gages should be evaluated on a case-by-case basis.
The gage length should be as small as possible to minimize effects of non-uniform PCA strain gradients. How- ever, strain gages should be large enough so that small IPCa features such as conductors and vias do not affect the strain reading. Figure Stacked Rosette Strain Gage. For strain measurements at varying temperatures, the Coefficient of Thermal Expansion CTE of the strain gage is not criti- cal so long as the gage factor is stable in the temperature range.
However, if this is not the case, the CTE of the strain gage should be matched to the printed board substrate. Strain gages with or without pre-attached lead wires can be used. Selection should be based on preference and specific applications.
Strain gages with pre-attached lead wires have the advantage of not requiring lead wire soldering, but it can be more diffi- cult to maintain a high quality bond line during strain gage attachment. Lead wires can be re-soldered but the bond line cannot be re-done. Conversely, manually soldered lead wires could result in electrical shorts. Lead wire soldering is best performed under a 20 - 50X optical inspection microscope.
Local bending near components will create variations in gage readings. For this reason gage placement must be precise. Wherever feasible the gages should be placed as described below. If the preferred location cannot be used, then strain guid- ance developed using the preferred location is not applicable. In this case, additional risk evaluation methods i.
Grid strains e1 and e3 in Figure should be e1 a Figure Recommended Gage Placement for BGA Components Grid strain e2 in Figure should be oriented diagonally away from package, with respect to the edges of the package. The consistent and precise placement of gages is critical to correlation of data between test location and samples. The distance between the gage and the BGA components might vary at each corner due to varying constraints. In such instances, gages should be placed as close to the preferred placement as possible.
This information should be indicated in the test report, including photographic documentation. Gage placement should be precise and consistent. In the event that another component, hole, or other obstruction interferes with the preferred placement, a single strategy should be employed as an alternative.
Examples are discussed in the following paragraphs. There may be situations where strain gages are not necessary on all corners of a device, such as when two or more devices are immediately adjacent or banked. In such instances, employ analytical techniques or computational models to identify the locations of the highest strain, thereby reducing the number of required strain gages.
All supporting assumptions and analy- sis must be clearly documented in the test report. It is recommended to provide a keepout area around components, where possible, to allow for strain gage placement and to reduce board flexure near components. However, there may be situations where strain gage placement is limited mechani- cally. Examples of such situations are illustrated in Figure and Figure In such instances, removal of part of the component may be considered as an alternative of last resort.
In this case, when removing the corner of any component, the gage should be placed so that its centroid is placed on top of the corner land pad on the PCA. The alignment of the strain gage rosette should be such that grid sensing element directions e1 and e3 are. Grid sensing element direction e2 should be oriented along the package diago- nal. This alternate placement is illustrated in Figure It is important to note that corner cutting changes the package geometry and mechanics and does not represent typical boundary conditions.
If this method is used, additional evaluation methods are needed such as destructive failure analysis to fully assess the risk. The removal of the component should be limited to what is necessary to facilitate the placement of the strain gage. An example is illustrated in Figure In the event that two gages at the corners of adjacent compo- nents would overlap, the test should be conducted using mul- tiple PCAs.
It is suggested that all corners of the component be gaged on the same PCA. To assess the risk to chip-level non-leaded ceramic compo- nents, uni- or tri-axial strain gages may be used. The preferred placement is with the gage substrate edge no more than 1. An example of this is shown in Figure Placement Proper board preparation will help ensure the proper bonding of strain gages; this will, in turn, improve the accuracy of the readings.
Strain gage attachment should also be performed in accor- dance with instructions provided by the strain gage and adhe- sive suppliers. Note that strain gages require the use of spe- cially formulated adhesive systems. For details, check with Within 1 mm your strain gage supplier. Recommendation for board preparation and attachment of the strain gages is as follows: Prior to strain gage placement, prepare the surface to ensure proper adhesion.
Desolder small components and discrete components that interfere with gage placement. Clean the surface with a solvent, such as Isopropyl alcohol. Solvents used shall be chemically clean. Once the surface has been prepared, attach the strain gages using the appropriate adhesive system.
A two-wire quarter bridge doubles the desensitization of the strain gage, can introduce a significant amount of temperature sensitivity due to leads, and creates a potential balancing issue for the instrumentation.
For the most stable static measure- ments, a three-wire system should be used. As lead wire routing is typically most constrained in ICT fixtures, lead wires must be routed in such a way as to avoid inter- ference with supports and push-down posts when the fixture is engaged. An example of lead wire routing is illustrated in Figure If the same test board is used for both ICT and BFT, lead wire routing must accommodate the footprint of the mechanical support and pins for both fixtures. Single solid copper wires can help facilitate routing in ICT fixtures, and also help mini- mize vacuum leakage.
Alternatively, ICT fixtures can also be designed to better accommodate the routing of lead wires. Some considerations are presented in Appendix A. Reinforce the lead wire attachment at each strain gage with epoxy or tape. Use adhesive-backed polyimide film or fiberglass cloth.
All sampling must be simultaneous, as sequential sampling may result in miscalculated strain values. In cases where this is not possible, a minimum scan frequency of Hz is recommended.
A minimum sampling resolution of 12 to 16 bits is recommended. Adjust signal amplifier gain for optimum use of dynamic range that is, maximize the gain, but set it low enough to prevent clipping of peak strain values. It is a good practice to use a data acquisition system that has built-in low pass filtering to remove noise during strain gage data collection. If the data appears truncated, the measurement frequency should be increased to verify there is not a high frequency dynamic event occurring.
Additionally, the number of available monitoring channels limits the number of measurements in any one pass. While mul- tiple passes are allowable if there are insufficient channels, all three gages in any stacked rosette must be monitored at the same loading. Since the printed board material has low thermal conductivity, gages are more likely to heat up due to the electrical current passing through them.
In general, an excitation level of 2V should provide satisfactory performance. As many of the procedures above can lead to errors in measuring the PCA strain, proper calibration of equipment will ensure the accuracy of the readings.
One method of calibration is the use of a simple calibration jig. Such jigs can be used to find and eliminate many errors due to gage placement, gage attachment, data acquisition system setup, and lead wires. One example is shown in Figure In this jig, a coupon board is deflected in steps by the insertion of shims. The strain for each shim is recorded and can be compared against expected variation. The fixture is only meant to check for basic errors in gage attachment and measurement.
It cannot be used to capture dynamic sampling rate errors, nor does it check for errors associated with the actual manufacturing equipment, i.
This is an integral part of IPCa strain gage testing. It is important that in-process handling is adequately Figure Example Gage Correlation characterized. This can be achieved by carefully replicating observed han- Tool dling processes, and the simulation of worst case handling. Such tests are intended to help identify weaknesses in the printed board, and to help optimize handling practices and fix- ture design. Where possible, proper handling procedures should be followed in order to minimize printed board flexure and appropriate fixturing should be used to handling boards between various process steps.
Strains imposed would be representative of nominal loads exerted during manufacturing, assembly, and test. The suggested procedures enables board manufacturers to conduct required strain gage testing independently, and provides a quantitative method for measuring board flexure, and assessing risk levels.
The topics covered include: Test setup and equipment; requirements; Strain measurement; Report format. Committee s : JC , JC Free download.
Registration or login required. The Board Level Cyclic Bend Test Method is intended to evaluate and compare the performance of surface mount electronic components in an accelerated test environment for handheld electronic products applications. The purpose is to standardize the test methodology to provide a reproducible performance assessment of surface mounted components while duplicating the failure modes normally observed during product level test. This is not a component qualification test and is not meant to replace any product level test that may be needed to qualify a specific product and assembly.
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