Thermoplastic vs Thermoset polymers 2. Thermoset polymers Thermoset polymers are popular for semiconductor packaging. For example, underfill, epoxy mold compound (EMC), etc. Before curing, liquid with a low viscosity • highly processable • usable for dispensing, coating, etc. starting materials (for example, resin) After full curing, stable networked structure high mechanical stability Thermoset polymers for semiconductor package ◊ Popular thermoset resins: epoxies, phenolics, acrylates, and bismaleimides ◊ Good properties for packaging • Low viscosity in the uncured state • Wide range of cure profiles various options for process - thermal and UV cure - partial cure (B-stage) ◊ Tailored modulus depending on the application rigidity ◊ Low thermal expansion coefficient ◊ Low moisture absorption ◊ High temperature stability ◊ Suitable for use with fillers (silicas, silver, etc) d inorganic . Polymer in general Glass transition temperature (Tg) Polymers are classified as glassy when their molecular backbones exhibit the inability to move and remain “frozen” in crumpled immobile conformations. Below Tg, upon heating only thermally induced expansion between the molecules occurs. Above Tg, the polymer observe liquid-like “flow” with the molecular chains gaining rapid ability to move freely. liquid 로드 중… reversible . _ ← rigid Strong . brittle . https://compositeskn.org/KPC/A102 Polymer in general Can bear much pressure . 가장급격히 변화 . 인 ㅣ O Above Tg, the polymer becomes soft, unable to bear loading. Below Tg, it becomes rigid, able to bear loading. At temperatures above Tg, a substantial reduction in Young’s Modulus (E) is observed between the stiff glassy state and the softened rubbery state. Polymer in general Viscosity → 점성 . 로드 중… Whereas the viscosity of a thermoplastic drops exponentially but monotonically with increasing temperature, thermoset resins behave in a more complex fashion. Initially, viscosity drops in the same manner as a thermoplastic, but once cure kicks off, the increasingly higher molecular weight and crosslinked polymer structure Curing process During the curing process (increasing temperature, exposure of UV, etc), the thermoset polymer undergoes polymerization and transitions from a flowing liquid resin into a rigid polymer. 단창체간 Chuin Two polymerization reactions are taking place in this process: 1. Linear polymer chains form and grow with the joining together of short monomers 2. Crosslinks form between the linear polymer chains (Thermoset polymers used in composites are most often are synthesized by a chemical reaction between two substances: resin and the hardener (crosslinking agent)). In these cases, crosslinks between the resin polymer chains are created by addition reaction of the crosslinking agent. O 형성 Chain 간 상호 연결 , Viscosity changes: thermoplastic vs. thermoset Thermoset Viscosity Viscosity 이명성 No Thermoplastic ⑦ . crosstink reversible Temperature . . Viscosity of thermoset polymers Initially, resin viscosity drops as a function of increasing temperature. Countering this resin viscosity drop, the thermoset crosslinking reaction takes place with elevated temperature and sees increasing molecular weight and restriction in mobility of the polymer – resulting in a corresponding increase in resin viscosity as the thermosetting reaction progresses. During a heated cure cycle, the resin therefore experiences the following sequence: key component of epor, 1. An initial lowering of resin viscosity as the resin is being heated, this is quickly countered and overtaken with, 2. An increasing resin viscosity due to the thermoset reaction Gcuriny effects. 3. Resin viscosity will continue to increase until the resin reaches the gelation point, where it takes on the behaviour of a semi-solid. . These two competing factors (temperature, and DOC – resin reaction) affecting resin viscosity must be balanced for setting the resin’s processing window. ∅ Material 성실달라짐 different structure . Gelation Changes in viscosity and modulus during curing Gelation is the incipient point of a cross-linked network. The thermoset polymer loses its ability to flow. Thus gelation defines the upper limit of the work life. 이geletationpoint이후로계옥 일어남 curng o As the cross-linking reaction proceeds to some degree, the molecular weight increases and hence viscosity will increase. At the gel point, all the chains become linked together into infinite molecular weight and thus infinite viscosity. The gel point also coincides with the first appearance of a mechanical modulus. But the gel point does not mean the end of curing. Curing continues beyond the gel point. 지 일어나는 변화 . 터 Avisosit Viscous flow Viscosity 대신 modulus 얻음 . o Rigid d As gelation continues, hook s modulus increases. ' Gel point law 만족 . solid . . Vitrification Modulus 등장 , e In thermoset curing, vitrifcation is the development of the glassy state as the curing reaction increases the Tg to the cure temperature. Vitrification occurs when temperature Tg = Tcure. IG process tempercnture . - - For thermoset polymers, the starting material is small molecules, which is usually liquid at room temperature. That means that Tg is much lower than room temperature. As curing proceed by increasing temperature, crosslinking between the molecules will proceed, which changes the state of the material to a rubbery state and increases the material’s Tg. For example, suppose that one cure a thermoset polymer (initially at liquid state) at an elevated temperature (curing temperature) and held it there for a long time. Then the reaction will take place; as crosslinking starts to occur, the material changes to a rubbery state. That means the Tg of the material has increased. As the curing time continues, at one point, the Tg reaches the curing temperature. That means that the material’s state has changed to a much crosslinked state and thus most of the material changed to the glassy state. That is vitrification. → 물질마다 → ㅇ 레데이게 정해림 T g Tcuri 얘랑 같아지면 & ng 로드 중… Cuvrng 거치면서 변함 T g Tcuri ng material 성질변함 Tg=Tcurin ← . glass . g ∅Characteristics of thermoset polymers : State of curing Uncured (A-staged) 낮은 점성 Partially cured (B-staged) Fully cured . ◊ Liquid with a low viscosity Good for dispensing ◊ Viscosity can be tailored by adding fillers ◊ Used for die attach pastes Characteristics of thermoset polymers : State of curing Uncured (A-staged) Partially cured (B-staged) 중간단계 Fully cured No return . , regid A . 고논에서 ◊ B-stage: crosslinking reaction (curing) is stopped at temperature sufficiently 、 below gel point ∅ µThe material is able to flow and resume curing upon additional heating. → Still abletoflow ◊ The material at this stage can be supplied in the form of film and coated onto a carrier. (Die attach film) It becomes sticky when heat is supplied during pick-place operation. . rigid Thermoset polymers Resin Mold Compound → EmC - Epoxy Epoxies - Acrylate monomers, oligomers - Acrylates and methacrylates - Bismaleimides - Hybrid resins (i.e. epoxy on one end double boud and acrylate or bismaleimides on the other end) . + Hardener Example of thermoset polymers: Epoxy ◊ 1,2-epoxy groups are diepoxy molecules in prepolymer. These groups react with amines or anhydride groups (hardener) by step reaction curing (crosslinking) ◊ Dimensional stability during cure (low shrinkage), almost no outgassing ◊ Excellent mechanical properties (good hardness, impact strength and toughness) ◊ Excellent Adhesion Z 이두개 √ √ Diglycydyl ether of bisphenol A (DGEBA) adhesion Cross-linking between chains chain 들간 . 접착제 Back-bone odeteronines mechanical stability . 끝날 Epoxy O ㅇ two ans Dcnam . N 있으면 ∅ O ' 아민 ' Hardenen . \ [Chemical reaction producing thermosetting polymers typified by epoxy resins] In this group of materials, the epoxide group (Scheme 6.4), is opened and used to link monomers. Epoxy resin adhesives normally come as two-part mixes. The resin component contains small and medium-sized molecules with an epoxy group at each end, called diepoxy molecules (Schemes 6.4b and 6.4c). The resin is set by adding a crosslinking agent, or ‘catalyst’. This material is a diamine (Scheme 6.4d). These join the epoxy-containing molecules together to form a strong cross-linked network. Once the network has been formed it is very difficult to disrupt. Note that there is no reaction product on polymerization, which means that only a small dimensional change occurs as the precursors harden. This is of importance in applications where shrinkage or expansion would create difficulties ↓ ↓ hardener 물 부산물 X . epo×y 는 이런이 > Example of thermoset polymers: Epoxy ◊ Mixing the resin with hardener (amines, anhydrides) will open the ring of the 1,2-epoxy group and start crosslinking between the chains. Resin O Hardener ① 끝지점 Amines Anhydrides Conventional semiconductor package Board assembly-based categorization λ chip encoapsulate 연결 , I IC Board ) PCB 보드에 올리기 = assembly . ussembly ↑ 컴퓨터 조립 X Board assembly-based categorization IC assembly-based categorization 지금은 작안쓴 _ priiitive Vs _ O . Jartom uagng d ⇐ Wafer 공정단계에서 d (Advanced Package) , Board assembly 중간에 flat end Solder £ Cu pad Surface mount assembly Through-hole assembly 면 Plated through hole (PTH) Cu pad PTH: Attach the die on PCB mechanically and electrically 연결 Solder Through-hole assembly PT H PC B 구멍채럼녹아서 θ _ Through-hole package 양쪽 Single In-Line Package (SIP) 한쪽 , Dual In-Line Package (DIP) . > _ O (hip : - pin wive bonding Lead frame .
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