{"id":"hbm-stack-assembly-test","level":"package","name":"HBM stack assembly, repair and staged test","shortName":"HBM stack assembly, repair and staged test","role":"Combines screened memory dies into a delivered stack using a specified joining route.","description":"An HBM stack is assembled from memory dies that have already passed substantial wafer processing and screening. Thin dies are aligned and joined so vertical connections continue through the stack. SK hynix’s public MR-MUF description combines mass reflow joining with molded underfill; thermocompression-based flows use a different joining sequence and material arrangement. The atlas labels these alternatives instead of mixing their steps into one recipe. Testing can occur at die, partial-stack, completed-stack and final-package boundaries, with coverage shaped by available access. Qualification releases a product/process configuration; it is distinct from screening every stack produced on that route.","specs":[{"label":"Incoming quality","value":"Conditional quality after defined screening","context":"Raw DRAM wafer yield has already affected available die count."},{"label":"Test boundaries","value":"Die, stack and final package","context":"Each boundary adds or observes different failure opportunities."}],"interfaces":[{"name":"Screened thin dies and base","direction":"in","signal":"Known genealogy, compatible interfaces and assembly materials"},{"name":"Tested HBM stack","direction":"out","signal":"Defined capacity, interface behavior and release status"}],"tradeoff":"Earlier test can avoid consuming good parts in a bad assembly but needs test access and adds handling/time; later test observes more completed interfaces.","whyAI":"A logic die cannot become a memory-equipped accelerator until compatible good stacks are available in the required quantity.","related":["known-good-die-test","bump-thermocompression-assembly","hbm-tsv-reveal","cowos-s-silicon-interposer"],"sources":[{"title":"SK hynix — Small Size, Big Impact","url":"https://news.skhynix.com/en/small-size-big-impact/"},{"title":"Advantest — Semiconductor test glossary","url":"https://www.advantest.com/en/investors/ir-library/glossary/"},{"title":"DISCO — Tech Briefing 2023","url":"https://disco.co.jp/jp/ir/movie/doc/E_Tech_Briefing_2023.pdf"},{"title":"Micron — HBM3E volume production begins","url":"https://investors.micron.com/news/press-release/2024/Micron-Commences-Volume-Production-of-Industry-Leading-HBM3E-Solution-to-Accelerate-the-Growth-of-AI-02-26-2024/default.aspx"}],"scale":"DRAM cell to vertical stack; routes and logical mapping are separate","kind":"integration","branch":"Memory / HBM fabrication and assembly","subbranch":"HBM manufacture: cell to stack","mechanism":["Select compatible screened dies and retain their identity and repair/bin status.","Align supported thin dies and establish vertical joint continuity using the named assembly route.","For the MR-MUF example, distinguish collective reflow from the subsequent protective molding/underfill role.","For a thermocompression alternative, preserve its actual joining and material sequence instead of borrowing MR-MUF order.","Perform the defined intermediate/final tests and count released stacks separately from qualification samples."],"misconception":"Multiplying raw die yield through a stack of already screened dies double-counts losses and misstates incoming quality.","check":{"question":"What yield term belongs after an inventory of known-good dies has already been counted?","options":["An assumed perfect finished-stack yield","New assembly losses and residual conditional incoming defects","The same raw wafer yield applied again to every die"],"answer":1,"explanation":"The population at the input boundary determines which losses remain to be modeled."},"science":[{"title":"Assembly-stage yield","equation":"N_out = N_ready × ∏ᵢ y_i","explanation":"N_ready counts complete compatible input sets after screening; each y_i is conditional survival through a new stage.","assumptions":"Stage factors require defined populations and nonoverlapping losses. Rework, repair and shared-cause failures need explicit branches."}],"prerequisites":["known-good-die-test","temporary-carrier-thinning","hbm-tsv-reveal"],"learningObjective":"Trace a named HBM assembly route and place screening at valid population boundaries.","workstream":"W06","visualFamily":"hbm-detail","engineeringExample":"Synthetic inventory: 100 complete sets of screened dies encounter two new stages with 0.98 and 0.97 conditional survival. Expected output is 95.06 stacks before other losses, without reapplying original wafer yield.","evidenceNotes":"No vendor stack-yield, repair coverage or process recipe is asserted. Stack qualification and current volume status must be supported separately.","labId":"engineering","scope":"Propagate conditional assembly and final-test survival from already screened inputs; test coverage and common-cause failures require separate evidence.","deepLabId":"assembly","investigationId":"manufacturing","labScope":"Propagate conditional assembly and final-test survival from already screened inputs; test coverage and common-cause failures require separate evidence."}