Puas Muaj Kev Tshaj Tawm -Kev Kho Mob ntawm PFA Rhaub Txhim Kho Nws Cov Kev Tiv Thaiv rau Lead- Dawb Soldering Fluxes?

Lead-dawb soldering fluxes (uas feem ntau muaj rosin, organic acids (succinic, adipic, glutaric) thiab halide activators (amines, bromides)) yog corrosive rau PFA ntawm qhov kub thiab txias (250-350℃). Cov seem ntawm cov dej ntws tawm ntawm PFA cov cua sov sheaths txhawb kev tawg, o thiab nkag mus sai. Thermal annealing (post-kho kho) ntawm PFA cov cua sov-feem ntau 200℃rau 4-8 h-nce crystallinity ntawm 40-45% mus rau 55-60%. Qhov siab dua qhov crystallinity, qhov qis dua qhov ntim amorphous muaj rau flux absorption thiab tshuaj tua kab mob. Lub annealed PFA yog 40-60% ntau resistant rau cov hlau lead dawb flux quab yuam tshaj lub unannealed PFA raws li qhia los ntawm qhov nce nyob rau hauv lub hardness thiab tawg lub sij hawm pib. Annealing tshem tawm cov teeb meem kev tsim khoom seem uas ua rau muaj kev ntxhov siab ib puag ncig (ESC). Rau yoj soldering los yog reflow ncu nrog cov PFA tso cua sov rau cov vapors flux, qhia meej tias annealed PFA tuaj yeem ua rau lub cua sov 2-3x.

Mechanism ntawm Flux nres thiab cov txiaj ntsig ntawm annealing
Lead tsawg fluxes yog nruj dua li cov hlau lead raws li cov fluxes vim yog qhov kub thiab txias ntau dua (260℃vs . 220℃) thiab ntau cov organic acids. Ntawm 260℃cov flux vapors condense ntawm qhov chaw txias xws li PFA cua sov. Cov organic acids permeate rau hauv cov cheeb tsam amorphous ntawm PFA thiab ua rau o (2-5% ntim nce) thiab plasticization. Cov halide activators catalyze saw scission thiab qhov hnyav molecular yog qis dua. Qhov tshwm sim: Nto tau nplaum, ces tau tawg me me, ces hlwv. Lub ntsiab barrier yog PFA crystallinity. Crystalline domains yog impenetrable rau flux molecules, tsuas yog amorphous domains tso cai rau diffusion. Kev nqus dej yog txo qis raws li qhov txo qis ntawm amorphous ntim los ntawm 27% thiab crystallinity nce ntawm 45% mus rau 60%.

Tom qab kho anneal ntawm 200 C (hauv qab PFA melting kub ntawm 305 C) reorganises amorphous chains rau hauv crystalline lamellae. Nws nthuav cov crystallites tam sim no thiab tsim cov tshiab. Qhov nce hauv crystallinity yog nyob mus ib txhis tshwj tsis yog PFA remelted. Annealing kuj txo qis cov kev ntxhov siab uas seem (saib Tshooj # 41), uas ua rau cov khoom tsis tshua muaj kev ntxhov siab rau ib puag ncig. Flux txo qhov kev ntxhov siab ntawm qhov nyuaj PFA nto. Kev ntxhov siab pab txhim kho qhov tsis kam ua kom tawg hauv PFA.

Lead-Free Flux Attack Resistance piv
Crystallinity (%) Qhov Mob PFAResidual Stress (MPa) Lub Sijhawm rau Nto Cracking nrog 260℃ntws vapor (hr) o tom qab 100 hr (%) Hardness nce tom qab 100 hr (Shore D)
Unannealed (raws li -extruded) 42 rau 46 4 rau 6 50 rau 100 3 rau 5 +8 rau 12
Annealed (200 degree, 4 teev) 52-56 2-3 120-200 1.5-2.5 +4-6
Annealed (200 degree, 8 teev) 56–60 1–2 200–300 1–2 +2–4
Annealed (220℃, 4 hr) 58–62 1–2 250–350 1–2 +2–4 (degradation risk)
High crystallinity resin (tshwj xeeb) + annealed 60 - 65 1 - 2 300 - 500 1 +1 - 2
Resin, siab crystallinity, unannealed 55–58 4–5 150–250 1.5–2.5 +3–5 Flux Resistance Testing Methodology
Siv cov kev sim hauv qab no kom tsim nyog PFA cov cua sov rau cov hlau lead- kev pab dawb soldering:

Tshaj tawm PFA cov qauv mus rau 260℃flux vapor rau 100 teev. Piv txwv li, siv cov pa tsis muaj- ntxuav flux (xws li Kester 951 lossis Alpha OM-340) hauv lub tank kaw nrog PFA cov qauv raug tshem tawm saum cov kua dej. Tuav ntawm 260℃± 5 degree.

Cov qauv tawm. Ntsuas.

Surface hardness (Shore D) yuav tsum nce<5 units

Qhov hnyav hloov -<0.5% (swelling or extraction)

Kev soj ntsuam pom hauv qab 20 × magnification - tsis muaj kab nrib pleb, hlwv, tackiness.

Khoov xeem (180℃nyob ib ncig ntawm 10 mm mandrel) Annealed kuaj yuav tsum khoov yam tsis muaj cracking, unannealed kuaj tej zaum yuav qhia microcracks.

Cov kev qhia tshwj xeeb yuav tsum tau: "PFA lub rhaub yuav tsum tau muab tso rau ntawm 200℃rau min 4 teev tom qab extrusion, nrog cov ntawv pov thawj crystallinity nce ntawm min 10 feem pua ​​​​cov ntsiab lus." Thov DSC cov ntaub ntawv los qhia txog crystallinity ua ntej thiab tom qab annealing.

Wave Soldering Field Experience
Lub PCB sib dhos ua haujlwm ua haujlwm PFA cov cua sov hauv lawv lub tshuab yoj yoj kom cov dej ntws ntawm 260℃kub. Tus qauv (unannealed) PFA cov cua sov ua tsis tau txhua txhua 6-9 lub hlis vim muaj qhov cuam tshuam los ntawm qhov tawg. Cov nroj tsuag hloov mus rau tom qab kho (annealed) PFA cua sov los ntawm tib lub chaw tsim khoom. Cov cua sov annealed kav 18-24 lub hlis, 2.5-3 × ntev dua. Tus nqi nce ntxiv (15-20% tus nqi) tau them rov qab hauv 6 lub hlis nrog kev hloov pauv qis dua thiab lub sijhawm poob qis. Cov nroj tsuag tam sim no xav tau kev sib tsoo rau txhua lub tshuab cua sov PFA hauv kev pabcuam flux.

Kev txwv thiab thaum Annealing tsis txaus
Annealing nce qhov tsis kam mus rau flux, tab sis tsis tiv thaiv PFA. Tsis muaj fluoropolymer yog siv tau rau cov kua dej tas mus li (immersion) raug ntawm 260 degree, siv ceramic lossis titanium heaters. Annealing yog zoo rau vapor exposure thiab intermittent kua sib cuag. Txawm tias annealed PFA yuav ua tsis tau nyob rau hauv tsawg dua 500 teev rau hnyav halide fluxes (siab bromide concentration). Nyob rau hauv cov xwm txheej no siv PFA coated hlau rhaub (hlau muab rov qab- tiv thaiv), los yog quartz rhaub nrog PFA fittings.

Tab sis annealing kuj muaj kev lag luam tawm -tawm. Cov crystallinity siab dua txhais tau tias tsis yooj yim thiab cuam tshuam tsis kam (elongation ntawm kev tawg txo los ntawm 300% mus rau 200-250%). Nyob rau hauv cov nqe lus ntawm tsis kam mus rau flux, unannealed PFA tsis zoo li, tab sis rau cov cua kub ntsiab, mechanical shock (kev pab cuam, portable wands), unannealed PFA yog zoo dua.

Xaus: 2-3 × loj dua flux tsis kam tom qab annealing.
Tom qab- kho thermal annealing ntawm PFA cua sov (200℃, 4-8 h) txhim kho cov crystallinity ntawm 40-45% mus rau 55-60%, piv txwv li cov ntim amorphous txo los ntawm 25-30%. Ntxiv crystallinity txhim khu kev tiv thaiv rau cov hlau lead-dawb soldering flux nres los ntawm 2-3X . Lub sij hawm rau nto tawg nce los ntawm 50-100 teev mus rau 200-300 teev nyob rau hauv vapor raug. Annealing kuj txo cov kev ntxhov siab seem, uas txo qhov cuam tshuam rau ib puag ncig kev ntxhov siab tawg. Rau yoj soldering, reflow ncu, los yog ib daim ntawv thov qhov twg PFA raug rau flux vapors ntawm 250-300 degree, qhia meej annealed PFA. Tus nqi ntxiv yog tsim nyog los ntawm lub neej ntev dua thiab qis dua lub sijhawm. Thaum txawm annealed PFA ua tsis tiav ntxov. Hloov cov khoom siv cua sov. Tab sis rau feem ntau cov kev pabcuam flux, qhov sib txawv ntawm kev hloov pauv peb lub hlis twg thiab txhua xyoo yog vim kev sib tsoo. Anneal nws. Los yog muab koj cov peev nyiaj kho mob. Koj qhov kev xaiv.