In IC packaging plants and SMT production lines, \"warping\" is one of the most common dimensional problems encountered by engineers. A piece of freshly baked BGA package looks normal in appearance, but when it is scanned on the measuring table, it is found that the amount of warping has exceeded the specifications. The next step is to track down the cause, change the process, and re-send the test... Many packaging factories have gone through this process more than once. Starting from the basics, this article explains what Package warping is, why it occurs, how to measure it, and what are the practical consequences of excessive warping.<\/p>\n\n\n\n
Package warping (Package warping) is the deformation of the IC package body that deviates from the plane. Mismatches in the coefficient of thermal expansion (CTE) of the material, the laminated structure and the thermal history of the process may all affect warping. Warping may change the relative position of the BGA contacts, increasing the risk of open circuit or bridging after backsoldering.<\/p>\n\n\n\n
IC packages usually contain silicon wafers, substrates, and sealants. The coefficient of thermal expansion, thickness and rigidity of each layer are different, and they will be bound to each other when heated or cooled, resulting in stress and deformation. The curing and shrinkage of the sealing glue may also affect the morphology at room temperature.<\/p>\n\n\n\n
The heating and cooling of reflow soldering will change the relative deformation of each layer. The actual peak temperature should be set according to the component specifications and assembly conditions.<\/p>\n\n\n\n
The amount of warping is affected by the package size, material, lamination and thermal history, and should be compared under specified measurement conditions.<\/p>\n\n\n\n
The following describes the two cross-sectional topologies with the same measuring surface and observation direction.<\/p>\n\n\n\n
Central bulge: Under the specified measurement surface and observation direction, the center of the package is higher than the corners.<\/p>\n\n\n\n
Concave center: Under the same observation convention, the center of the package is lower than the corners.<\/p>\n\n\n\n
The warping direction of the same package may be reversed with temperature. When comparing charts, the measurement surface, observation direction, and sign convention should be marked.<\/p>\n\n\n\n
Room temperature measurement provides static deformation data, which can be used for comparison before and after incoming materials, shipment quality control or testing. To understand the warping changes in the reflow soldering process, it needs to be measured separately according to the temperature history.<\/p>\n\n\n\n
The amount of warping exceeds the specifications, which directly affects the downstream SMT process and product reliability. Common problems include\uff1a<\/p>\n\n\n\n
Poor coplanarity of tin ball: Package deformation may change the deviation of the top of the ball relative to the reference plane, increasing the risk that some contacts will not be able to join normally. The allowable value shall be based on the drawing of the part number or the acceptance specifications of both parties.<\/p>\n\n\n\n
SMT air welding: The relative deformation of the package and the PCB during back welding may widen the internal bonding spacing and increase the risk of open circuit.<\/p>\n\n\n\n
Short circuit or bridge: The other extreme is that warping causes some tin balls to squeeze excessively, forming a bridge short circuit. It is more obvious in the Fine Pitch package.<\/p>\n\n\n\n
Hidden dangers of reliability: The geometry and stress distribution of the solder joints may affect the fatigue life of the subsequent thermal cycle, and it needs to be evaluated in combination with the actual solder joints and the test results.<\/p>\n\n\n\n
Warping measurement methods are divided into two categories according to the contact method\uff1a<\/p>\n\n\n\n
Contact measurement (probe type): Use a mechanical probe to contact the measurement points in sequence to calculate the height difference. The disadvantages are that the measurement speed is slow, the probe risks damaging the sample, and it is difficult to obtain comprehensive 3D morphology data.<\/p>\n\n\n\n
Non-contact 3D contour measurement: The height data of the visible surface is obtained optically. The scanning range and splicing method are set according to the sample size, surface condition and resolution requirements.<\/p>\n\n\n\n
Non-contact 3D measurement can be used to compare the room temperature morphology of packages such as BGA, CSP, FCBGA, etc.<\/p>\n\n\n\n
Standard reference: JESD22-B112C covers the measurement of high temperature package warping of surface-mounted ICS. When measuring room temperature, the measuring surface, reference plane and warping calculation method should be recorded.<\/p>\n\n\n\n
Jinghong adopts Keyence VR-6200 surface 3D contour measuring instrument to provide non-contact package warping measurement services, which are mainly suitable for the following scenarios\uff1a<\/p>\n\n\n\n
Package type: Mainstream package forms such as BGA, CSP, QFN, QFP, FCBGA (static measurement at room temperature).<\/p>\n\n\n\n
Measurement items: evaluation of the overall warping quantity (warping), warping direction (concave\/convex), and coplanarity of the tin ball.<\/p>\n\n\n\n
Measurement conditions: Static measurement at room temperature, the morphology of room temperature before and after the reliability test can be compared according to demand.<\/p>\n\n\n\n
Wide-range scanning: the measurement area and splicing method can be planned according to the sample size and the required resolution.<\/p>\n\n\n\n
One-stop completion: Jinghong also has environmental testing capabilities (temperature cycling, etc.), and can complete the \"reliability test + comparison before and after warping measurement\" in the same place, saving time for cross-factory testing.<\/p>\n\n\n\n
If you need to know the scope of measurement capabilities, sample specifications or quotation, please contact Jinghong.<\/p>\n\n\n\n
Q1<\/strong>\uff1aIC<\/strong> Why is the package warped?<\/strong><\/p>\n\n\n\n Mismatch in the coefficient of thermal expansion of the material is a common factor. Package thickness, material rigidity, curing shrinkage and thermal history will also affect the size and direction of deformation.<\/p>\n\n\n\n Q2<\/strong>: How to improve the warping of the package?<\/strong><\/p>\n\n\n\n The direction of improvement usually starts from three levels: material selection (using a substrate or sealant closer to the CTE), laminated structure design (making the upper and lower CTES of the package more symmetrical), and process parameters (optimization of reflow soldering temperature curve). Measuring warping is only the first step, and the symptomatic improvement can only be achieved after root cause analysis.<\/p>\n\n\n\n Q3<\/strong>: Does the package warping measurement need to destroy the sample?<\/strong><\/p>\n\n\n\n The instrument obtains the surface height in a non-contact optical manner. If surface characteristics such as high reflectance require pretreatment, the sample will be confirmed before the measurement is suitable.<\/p>\n\n\n\n