Next Generation Molding Compound Materials for Flip Chip Matrix Array Molded Packages

Next Generation Molding Compound Materials for Flip Chip Matrix ArrayMolded PackagesLim Chong Sim a, Mun Leong Loke a, Kang Eu Ong a, Enrico Garcia a, Mohamed Syazwan Osman a, Leonel Arana b, Yoshihiro Tomita c, and Jiro Kubota ca Assembly & Test Technology Development – Malaysia, Kulim, Malaysiab Chandler Assembly Technology Development, Assembly & Test Technology Development, Chandler, Arizonac Pathfinding, Assembly & Test Technology Development, Tsukuba, Japanlim.chong.sim@Abstract—This manuscript describes the recent pathfinding and development activities on the molding compound for the flip chip matrix molded array (FCMX) platforms. The key focus of this manuscript is on the materials and packaging challenges associated with the high K molding compound and exposed second level interconnect molding. In addition the advantages and disadvantages of transfer and compression molding are discussed.1. IntroductionFCMX packages are the next generation of packaging technologies designed for the mobility and ultra mobility product segments. Over the last few years, the mobile computing technologies have evolved into increasingly complex systems, resulting in significant packaging challenges. The key challenges often associated with the FCMX platforms are strip warpage, which could potentially result in high yield loss for the downstream modules. High strip warpage may also leadto excessive package warpage, potentially violating the outgoing coplanarity specifications by the Joint Electron Device Engineering Council (JEDEC), which stipulates that a package with a ball grid array (BGA) pitch of < 0.5mm needs to meet an outgoing ball-coplanarity specification of under 100um.Various technology options have been explored previously to address the warpage concerns. This includes having the right media design to restrain the strips from warping during the assembly process flow. Although media acts as an effective restrainer, it is an expensive solution, which would typically require some level of compromise within the assembly process flowto enable integration of the media solution. Therefore from the manufacturability perspective, molding compound still remains as the most viable option for warpage controls.In this manuscript, discussions are focused on the molding compound issues and requirements for the different packaging technologies. Sections 3 and 4 are focused on flip chip matrix molded ball grid array generation 3 (FCMB3) high K molding compound development, while Section 5 focuses on the flip chip matrix molded ball grid array generation 4 (FCMB4) ultra long gellation compression mold formulation. In addition the different molding compound technologies that drive the formulation developments are described. 2. Background: Molding Compound Drivers 2.1. Generic Molding Compound RequirementsThe main function of molding compound is to protect the package from moisture, thermal and environmental exposure to ensure that it’s able to withstand its stipulated reliability requirements. In addition molding compound provides the package with the robustness for mechanical handling, packaging and assembly. Overall the molding compound requirements can be further summarized to the following key items:•Low moisture absorption – “Pop-corning”phenomenon occurs because of pressure buildingup from the out gassing of moisture within the packages during the level 3 preconditioning (L3P)stress resulting in interfacial or bulk fracture. In general, moisture absorption is lower for lower Glass Transition (T g ) resins such as the biphenyldue to the lower free volume within the cross-linked resins.•Adhesion to multiple interface – Good adhesion to multiple interfaces such as underfill, solder resistand silicon die is an important criteria to ensurethat there is no delamination between the interfacesduring assembly, which could result in crack propagation during temperature cycle stress.•Low cure shrinkage – One of the key factors affecting strip warpage is the shrinkage of the molding compound during curing. Cure shrinkageis defined by the differences between the total shrinkage with the thermal shrinkage.Given the contrasting differences in packaging architecture between FCMB3 and FCMB4 (to be discussed further in sections 3 and 5), a generic molding compound requirements is not sufficient tomeet the overall package performance. Therefore a significant amount of work was done to formulate different molding compound formulations to meet the competing needs of each packaging technology options.2.2. FCMX Packaging Roadmaps and TrendsFigure 1 shows the projected packaging trends for theFCMX platforms, which is based on the dimensional scaling of the transistor’s density and customer’s requirements. The key driver is the scaling of power delivery requirements due to an increase in transistors density in order to meet the customer’s request for an increase in functionality. This consequently results in an increase in junction temperature, which reduces the silicon performance. The other driver which is based on projected customer requirements is the dimensional scaling of the package Z height requirements, which results in a lower silicon thickness and a thinner substrate technology.Figure 1. Projected packaging trends for FCMX platforms.2.3. New or Complex Packaging TechnologyThe emergence of new and complex packaging technologies due to design constrains have resulted in a new set of molding compound requirements. Figure 2 illustrates the revisions in packaging architectures that the FCMB4 pathfinding platform has undertaken due to changes in the product specific roadmaps (PSR). In general, both the overmold and exposed second level interconnect packages are assembled using the 1269 silicon architecture on a high density interconnect (HDI) direct laser lamination (DLL3) strip technology, which is attained through the laminations of multiple build up materials with laser via [1]. The keyadvantages of the coreless DLL3 strip is the increase in signaling rates for high speed inputs outputs (HSIO) requirements and a reduction in the overall strip Z height. However this technology suffers from several drawbacks, including high warpage due to reduced thickness and absence of a core, which consequently results in yield loss at chip attach. The details on both the packaging technologies (1) Discrete over mold package and (2) Exposed second level interconnect molding will be discussed in details in the following sections.Figure 2. Revisions in FCMB4 Packaging Architecture2.4. Transfer vs. Compression MoldingTransfer molding has been Intel’s® legacy molding compound process for the Flip chip molded matrix array package 1 (FCMMAP 1), wire bonded and Flash platforms. However moving forward, the scalability for the transfer mold is at stake due to product requirements for a thinner mold clearance and lower temperature processing. Internal data collection on a package with 100um mold clearance indicated that the present transfer mold technology would be broken for molding compound with spiral flow <110cm as shown in Figure 3.Figure 3. Projected packaging trends for FCMX platforms.For the transfer molding process, molding compound pellets are placed into the plunger pots of the heated mold chase as shown in Figure 4. Once the mold compound is molten, the plunger transfers the molding compound through the runners into the cavity of the mold chase, and air in the chase cavities is vented out through strategically located venting holes. To ensure complete mold fill throughout the cavity of the mold chase, it’s important to define the right flow and melt viscosity properties. Nevertheless this is still a challenge for the high K molding compoundformulation because of the increase in melt viscosity with higher filler loading.Figure 4. Transfer molding bottom chase with plunger pots.The other known molding technique which was recently explored during the FCMB4 pathfinding is the compression mold. Compression mold shown in Figure 5 can be thought of as a runnerless mold system, because the molding compound is placed directly intothe cavity of the mold chase prior to clamping [2]. Thecompression molding technique is unique because of itsability to support both powder and liquid molding compound formulation. In addition compression mold has been demonstrated to be able to achieve thinner mold cap clearance. Compared to the transfer mold process, compression mold drives a reduction in through put time (TPT) with the omission of the molding compound transfer process shown in Figure 6.Figure 5. Compression molding bottom chase filled with mold.Figure 6. Potential TPT reduction with compression mold.From the materials perspective, compression molding drives a separate set of requirements compared to the transfer molding formulations. For instance lubricationwax is not required in the formulation because of the presence of mold film, which prevents the molding compound from sticking to the mold chase. In addition compression molding compound formulation typically requires a longer gelation time to enable it to flow and fill up the cavities within the mold chase.2.5. Critical Molding ParametersAmong the key critical factors for warpage reduction is design geometry, materials properties and processing conditions. From the materials perspective, keyproperties that influence the outcome of strip warpageare shrinkage factor, glass transition temperatures (T g ), coefficient of thermal expansion (CTE) and the modulus. Shrinkage factor is a dominant force for warpage control at room temperature, while the T g and CTE are crucial to controlling the dynamic warpage of the strips at reflow temperatures because of CTE mismatch.2.6. Test Vehicle ComparisonsVarious test vehicles (TV) were designed and taped out during the FCMB3 development phase and FCMB4 pathfinding phase as shown in Table 1. The key differences between both the platforms lie with the substrate technology used. FCMB3 Pinang TV is an LDI substrate with a core, while the FCMB4 Joslin 2 and Tonkin TV are DLL3 strips designed to meet the highdensity design rules. Due to the absence of cores, DLL3 strips are very flimsy, with high incoming warpage variations.Table 1. Test Vehicle comparison between FCMB3 and FCMB4.FCMB3 FCMB4 Attributes Pinang Joslin 2 Tonkin Die size 11 x 11mm 8 x 6mm 11 x 11mm Package size 13.8 x 13.8mm 13.8 x 13.8mm 13.8 x 13.8mm Substrate LDI DLL3 HDI DLL3 HDISilicon 1266 1266 1268 Ball pitch0.5mm 0.413mm 0.5mm3. High K Molding Compound forOvermolded Package80% Others MHSMold cure60%Clamp Injection3.1. Motivation for High K Mold Compound Technology Traditionally, for an over molded package (e.g FCMB3), the key challenge is to enable an effective heat dissipation path from the silicon to ensure that the overall package is meeting the TDP requirements. This is because any increment in temperature by a magnitude of 10-15o C above the T j limit of 110o C may result in a 2X difference in the lifespan of the device [3]. Technology roadmaps have projected that the future FCMX platform may be required to envelop products with power dissipations up to 35 Watts, thus emphasizing the need for an effective package and40%T i m e20% 0%Transfer moldCompression mold WB Compression mold FC Process material optimizationsystem level thermal solutions. Figure 7 shows that 90% of the heat generated by the silicon is dissipated through the board, and the remaining 10% dissipated to the surroundings via convection. This shows that molding compound could play an effective role in heat dissipation by virtue of providing a larger surface area for heat flow.Figure 7. Heat transfer path for a typical FCMX package.Thermal modeling in Table 2 has indicated that the conventional silica (SiO 2) filled molding compound formulation with a thermal conductivity value ofaround 0.8W/mK would not be able to meet the Thermal Design Power (TDP) targets for a 5 Watts power dissipation product. Instead a 3.2 W/m.K molding compound would be required.Table 2. T j max estimation based on 150um mold clearance.To increase its thermal conductivity, various thermally conductive ceramic fillers such as Alumina (Al 2O 3) and Silicon Carbide (SiC) were investigated. The additionof thermally conductive fillers adversely impacts themolding compound properties (higher CTE, higher modulus and shorter spiral flow). Therefore, the challenge lies in developing a thermally conductive molding compound technology, which is processable.3.2. High K Molding Compound FormulationsMarket survey on existing suppliers showed that the high K molding compound is a generally new formulation with low levels of market penetration within the industries. Therefore collaborations with several of the molding compound suppliers were formed to specially develop a formulation that will meet Intel’s thermal conductivity requirements of 5W/m.K. The key factors considered in the formulation were the choice of fillers and resin chemistries. For this a variety of ceramic fillers such as Al 2O 3, Silicon Carbide (SiC) and Aluminum Nitride (AlN) were all considered to enhance the thermal conductivity of the molding compound as shown in Table 3. Each of these fillers has their own sets of advantages and disadvantages. For instance although AlN fillers have the highest bulk thermal conductivity of ~270 W/m.K, it is still an unsuitable choice because of its hygroscopic nature which results in it being easily reversible into Al(OH)3 and ammonia (NH 3) under the presence of moisture [4].Table 3. Physical properties of thermal conductive fillers.Al 2O 3SiC AlN Density (g/cm 3) 4.00 3.22 3.26CTE (10-6o C -1) 7.60 4.51 4.40 Thermal conductivity (W/m.K) 30 220 270 Dielectric constant – 1MHz (k) 9.3 8.9 8.9 Young Modulus (GPa) 386 400 308As discussed in the previous sections, it’s important to strike a balance between the thermal conductivity targets with the flowability of the material. Figure 8 shows the correlation between melt viscosities and thermal conductivity. From the graphs it was established that the increment in filler ratio not only increases the thermal conductivity but also drives an increase in meltviscosities due to an increase in filler-matrix interactions. Some of the typical approaches used by molding compound suppliers to control the melt viscosities include selecting a lower viscosity resin to begin with.For this the biphenyl resin is somewhat a preferred option among the molding compound suppliers because of its low moisture uptake and good adhesion to multiple interfaces. In addition melt viscosities can be controlled by optimizing the filler distribution ratio and the hardener system used.1000Thermal conductivity Melt viscosity 6100Figure 8. Correlation between thermal conductivity and melt viscosity.Table 4 shows the list of all the molding compound materials which were evaluated during the FCMB4 pathfinding time frame. They include the X-43-3244-2 formulation, which serves as the baseline for data collection. The other formulations are the X-43-3248-1A and X-43-3248-1C, which were reiterations from the X-43-3248-1 formulation. The key differences between the materials lie in the filler systems used. To achieve a thermal conductivity of ~5W/m.K, the filler loading (wt%) of Al 2O 3 + SiO 2 fillers for the X-43-3248-1A formulation were increased from 75wt% to 77wt%,1030102030 40 Vol.% T h e r m a l c o n d u c t i v i t y (W /m .K )M e l t v i s c o s i t y a .s )(Pwhile for the X-43-3248-1C formulation, the SiO2 fillers were replaced with higher conductive SiC fillers. In addition silicone particles were added into the formulations to act to prevent excessive mold shrinkage during the curing process.Table 4. High K molding compound formulation comparison. Supplier(Materials)Material description Key propertiesShin-Etsu (X-43-3244-2) FCMB3 baselineMulti functional resin, 75Vol% Al2O3 + SiO2hybridT g – 183o CCTE 1/2 – 14/43ppmK – 3.2W/m.KSpiral flow – 88cmShin-Etsu (X-43-3248-1) Biphenyl resin, 75 Vol%Al2O3 + SiO2 hybridT g – 124o CCTE 1/2 - 13/53 ppmK - 3.2W/m.KSpiral flow – 127cmShin-Etsu(X-43-3248-1A) Biphenyl resin, 77 Vol%Al2O3 + SiO2 hybridT g – 120o CCTE 1/2 - 12/47ppmK - 4.3W/m.KSpiral flow – 78cmShin-Etsu(X-43-3248-1C) Biphenyl resin, 75 Vol%Al2O3 + SiC hybridT g – 122o CCTE 1/2 – 12/47ppmK = 4.7W/m.KSpiral flow – 70cmKyocera (G1250HT4) Low molecular weight,79% Al2O3 + SiO2 hybridT g – 130o CCTE 1/2 - 14/54ppmK = 4.6W/m.KSpiral flow – 105cmSumitomo (X80744) Biphenyl resin, 77 Vol%Al2O3 fillersT g – 130o CCTE 1/2 = 10/35ppmK = 5.0W/m.KSpiral flow – 90cm* All the data reported in Table 4 are suppliers’ data3.3. High K Molding Compound Assembly IssuesFigure 9 shows the overall process flow for the FCMB3 and FCMB4 over-molded package. The first step is to pre-bake the strips from underfill (CUF) module to drive off moisture, after which the out going strips is subjected to a plasma treatment to activate the surface in order to enhance the adhesion with the substrates. The following step is molding followed by a post mold cure to complete the cross-linking of the polymers.Figure 9. Assembly process flow for FCMB4/FCMB3 discrete overmold packages.One of the key challenges associated with the high K molding compound formulation is the significant increase in melt viscosity. As shown in Table 4, the molding compound viscosity increases significantly with an increase in filler loading. This may result in a range of issues due to the tight mold clearance between the die. In Table 5 mechanical models predicted that the mold cap requirements for a 5 Watts package needs to be < 100um thick if a 3.2W/m.K molding compound material were used.Table 5.T j max estimation for 10W power dissipation.Thermal conductivity (W/m.K)Moldclearance 0.8 3.2 5.0 10 20 250 um 179.4 116.1 108.5 101.8 98.4 150 um 145.6 107.7103.1 99.1 97.0 100 um 128.8 103.4 100.4 97.7 96.4 50 um 111.9 99.2 97.7 96.4 95.7 Besides incomplete fill, other key issues associated with the mold flowability are mold flow marks, shown in Figure 10. This phenomenon occurs only on molding compound formulations with very low spiral flow, (e.g X-43-3248-1A). Although flow mark may not have any known reliability implications, it may impact the 2 dimension unit identification (2DID) readability and may also fail the customers’ quality acceptance criteria. From the process perspective, lowering the molding temperature may help to improve mold flow marks. However the only complication is a potential reduction in adhesion.Figure 10. Mold flow marks on the strip after cure.3.4. Key Challenges: Excessive Strip Warpage Managing incoming strip warpage and subsequently keeping the strips flat throughout the assembly pipeline is the biggest assembly challenge for the FCMB4 platform. This is important; because high strip warpage has been known to interact with the downstream modules such as ball attach and saw singulation resulting in yield loss. Embedding glass cloths into the substrate build up layers helps to improve the overall strip warpage; but it’s still insufficient to drive the warpage below the limits acceptable by the downstream modules as shown in Figure 11. Mechanical modeling predicted that the glass cloth locations would have a certain degree of influence on the overall strip warpage. It was predicted that the Joslin TV with the bottom layer glass cloth would have the lowest strip warpage, followed by the center layer glass cloths. On the other hand, glass cloth layers also have its own set ofdisadvantages, including limitations on the package design rules and a higher cost target. In this section our discussions will center on the warpage response for the Joslin DLL3 1 layer glass cloth TV with different molding compound materials.Figure 11. Dynamic warpage for Joslin and Wilmot.Figure 12 compares the cluster level warpage ofShinEtsu X-43-3248-1C, Kyocera G1250GT-4 and the Sumitomo X80744 high K molding compound formulations. Warpage measurements on the incoming strips showed that the strips are warped in the ‘smiley’ directions. Once the post mold cured, the strip warpage increased in the ‘smiley’ direction for both the X-43-3248-1C and G1250GT4. This trend was nevertheless different for the Sumitomo X80744 molded strip, withthe warpage direction changing from ‘smiley’ to ‘crying’ after post mold cure process.Figure 12. Strip level warpage comparison at different process steps.As discussed, the strip warpage mechanism is typically influenced by the T g , CTE and modulus of the molding compound. One example is the increase in strip warpage along the smiley directions for X-43-3248-1C and G1250GT4 material. This is due to its low T g , which results in higher expansion of the mold due to the transformation from crystalline to a rubbery phase at temperatures above T g . In addition strip warpage is influenced by the mold compound shrinkage during the curing process. For example it is believed that the polymeric shrinkage of the X80744 mold during the curing process triggers a compressive force towards the substrate resulting in changes in warpage magnitude from “smiley’ to ‘crying’ as shown in Figure 13. To reduce the cure and thermal shrinkage, various reiterations have been previously investigated. This includes the addition of silicone micro phases which reacts with the resin system to expand the domains against the polymerization shrinkage.(4) Post (3) Post mold cure (2) Post mold(1) Post underfillFigure 13.Warpage mechanism at different process steps: (1)Substrate warp because of CTE mismatch with die (2) Infliction inwarpage direction after post mold cure because of mold shrinkage (3)Slight reduction in warpage because of relaxation in polymer chains with extended cure (4) Post singulation warpage.P o s t m o l d I n c o m i n g I n c o m i n g I n c o m i n g P o s t c u r e P o s t c u r e P o s t c u r e P o s t c u r eP o s t m o l d P o s t c u r e P o s t m o l d P o s t m o l d P o s t m o l d P o s t m o l d I n c o m i n g P o s t c u r e I n c o m i n g I n c o m i n g4. High K Mold Compound ReliabilityIssues4.1. IntroductionPassing the stipulated reliability stress test is an integral requirement for package certification. This requires the units to pass electrically (E-Test) at Level 3 preconditioning (L3P), and the subsequent readouts of unbiased highly accelerated stress test (HAST) 130o C/85%RH for 100 hours or temperature cycle profile B for up to 1000 cycles respectively. At every intermediate read out, the packages are screened with scanning acoustic microscope C-mode (CSAM) to check for any abnormalities at the interface.4.2. Reliability Fall OutsTable 6 lists the reliability data for the X-43-3244-2 molding compound at different reliability stress read outs. Two defects, namely mold-die delamination and mold cracking, were observed from the CSAM screening and will be discussed in further detail in the following subsections.Table 6. Reliability fall out for mold-die delam and mold crack . EOL L3P uHAST (50hr) TCB (500X) BHAST(2V)Mold-die 0/430 19/430 1/99 23/99 23/23Moldcrack0/160 0/160 0/80 34/80 NA4.3. Reliability Issues: Mold-Die DelaminationFigure 14 shows the CSAM and cross-section images on a unit with mold-die delamination after the L3P stress test. From the CSAM images, it was clear that mold-die delamination occurred only at the corners of the die. Cross sections revealed that mold-die delamination had a high potential risk of incurring electrical failures becauseof propagation along the mold to die path towards the mold-underfill interface.Figure 14. CSAM images of mold-die delamination (R) and cross section images of the delamination (L).The root cause for mold-die delamination is suspected to be a combination of poor adhesion and high peel stress at the corners of the die. This hypothesis was supported by the die thickness data in Figure 15, which concurred that the thicker dies (270um) have a significantly lower fall out than the thinner die (225um). The reason is packages with a thicker mold cap warps more due to the dominance of the molding compound, which exerts more peel stress at the corners of the silicon.Figure 15. X-43-3244-2 mold-die delamination fall out for twodifferent die thickness (225um and 270um).One of the solution paths considered to resolve mold-die delamination, was to increase the adhesion of the molding compound to the silicon interface. Therefore a new molding compound, X-43-3248-1, formulated with the biphenyl resin as its matrix, was brought in for further evaluation. Besides having good adhesion, thebiphenyl resin is also known to have low moisture uptake compared to the higher T g multifunctional resin. Figure 16 shows the results for the button shear test which was conducted after the post mold cure and L3P stress. The results showed that the X-43-3248-1 had adhesion strength in the magnitude of 30% higher compared to the X-43-3244-2 and the silica filled KMC2500VAT1. However the strength degrades marginally after the L3P stress test due to thermal degradation on the polymer matrix.Figure 16. Mold-die adhesion strength comparison between the X-43-3248-1 with the X-43-3244-2 and KMC2500VAT1.Table 7 shows the results for the X-43-3248-1 molding compound formulation at different reliability stress readouts. The result after L3P + uHAST 130oC/85%RH 100 hours is clean from any mold-die delamination. However when subjected to L3P + TCB500X stress, all of the 40 units loaded into the stress chamber failed for mold-die delamination based on CSAM inspections. This observation showed that the mold-die delamination defect observed on X-43-3248-1 molding compound is not moisture driven defect but is due to stress, aggravated by the low T g (124o C), which falls within therange of the TCB profile.Table 7. X-43-3248-1 fall out for mold-die delam.Mold compound EOL L3PuHAST(50hr)TCB (500X)X-43-3248-10/80 0/80 0/40 40/40Besides evaluating different molding compound formulations, equal focus was given to assessing the risk for mold-die delamination from the thermal perspective.Thermal modeling using the finite element method wascarried out to comprehend the gain in maximum junction temperature (T jmax ) if a delamination is present at the corners of the die. A sensitivity model for differentcumulative areas of delamination - 0.5%, 2%, 10%, 20%, 30% and 40% - was constructed to predict the minimum cumulative area of delamination that would be 270um/225um/490um 490umPost mold curePost L3P stress X-43-3244-2 X-43-3248-1KMC2500VAT1required before a significant rise in temperature will beobserved.The result for the sensitivity model shown in Figure 17, suggests that the rise in die corner temperature would be significant only if the total area of delamination for the four corners exceeds 10%, while the rise in die center temperature would be significant only if the total delamination area exceeds 40%. Therefore based on the modeling results, it was concluded that the thermal risk induced by the mold-die delamination defect is low, because none of the packages post reliability stress have a total delamination area exceeding 10%.Figure 17. Temperature rise at die center, die corner and mold top for different corner defects assumptions.4.4. Reliability Issues: Post TCB Mold-crackTable 8 quantifies the number of units with mold cracks at different reliability stress read out. The results showed that mold crack occurred only during the temperature cycle profile B (TCB) reliability stress test, which indicates that mold cracking is a thermo-mechanical stress induced defect. Visual observations in Figure 18 on all the CSAM images showed that the cracks initiate from the high stress edges of the 2DID and the Instruction set for execution (ISET) mark, indicating that flaw is pre-requisite for crack propagation to occur.Table 8. Reliability fall out for mold crack at different stress read out .EOL L3PuHAST (50hr)TCB(500X) TCB (1000X)Moldcrack 0/160 0/160 0/80 34/80 40/53Figure 18. Mold crack CSAM images at different stress read out.The key concern with mold cracking is the potential propagation of the crack length towards the silicon, which would result in units failing electrically due to die cracking shown in Figure 19. It was also observed that the units with mold cracks have resulted in mold-die delamination, which is a risk for thermal dissipation if the delamination exceeds 10% of the total area. To comprehend the root cause of mold cracking, a lab scale simulation GRC focusing on two possible root causes, molding compound formulation or laser mark depth was carried out as shown in Table 9. The motivation for including a non high K mold compound leg was to comprehend if the higher CTE of the high K molding compound could have induced more stress compared to a non high K mold formulation. This GRC was carried out by pre-heating the units on a hot plate at 300o C for 10 minutes before being soaked in liquid nitrogen for another 10 minutes to simulate the TCB stress test. This was repeated for a total of 4 cycles, with visual inspections being carried out for mold cracking after every cycle.Figure 19. Die crack from a post decap mold crack unit.Table 9. Lab scale GRC leg to decouple mold crack root cause.Molding compound Laser power (Watts) High K mold 1.43W 2.04W Non high K mold1.43W2.04WThe results in Table 9 showed that there was no mold crack observed for either the high and non high K molding compound after 4 cycles on the units marked with a 1.43 Watts laser power. On the other hand, units which were marked with a 2.04 Watts laser power showed mold cracking after 1 cycle of temperature simulation. This clearly showed that mold cracking is caused by the difference in mark depth induced by the different laser power. Hence it’s important to control the laser power and laser pulse of the 2DID to reduce the overall mark depth. The setback of doing so is the possible degradation in contrast for the 2DID readability.Therefore for risk mitigation, the other option, which was pursued without having to reduce the mark depth, was to move the 2DID mark away from the die shadow region to reduce the corner stress. This was based on the mechanical modeling quasi-static analysis, whichshowed that the higher stress region was within the die shadow because of the higher CTE mismatch between the mold-die compared to the mold-substrate interface shown in Figure 20.。