How do conductive particles connect along Z while staying insulated in XY? ACP or ACF — which process route fits which job? And why do two Japanese makers dominate the high-end ACF market? Plus a "ZJWY view": material selection, bonding parameters and acceptance criteria on the screen-repair bench.
An anisotropic conductive adhesive (ACA) conducts along the Z axis only. In paste form, applied on site by dispensing or printing, it is commonly called ACP (Anisotropic Conductive Paste); in film form it is the ACF (Anisotropic Conductive Film).
The core property in one sentence: insulating in the XY plane, conductive along the Z axis. The adhesive carries uniformly dispersed conductive particles (polymer microspheres coated with metal, a few microns across). During bonding, only the particles directly between opposing pads are trapped and their coating is crushed to form a connection; particles between neighbouring pads never touch each other, so the lateral direction stays insulating. One layer of material therefore provides mechanical bonding + fine-pitch connection + insulation at once — used for COG/FOG/FOB display bonding, camera modules, FPC connections and other ultra-fine-pitch applications.
Both work on the same principle. The difference is when the particle positions get fixed:
Selection logic in one sentence: ACP trades on-site application for low cost, fewer steps, heat-sensitive substrates and high-mix small batches; ACF trades pre-locked particles for ultra-high yield and ultra-fine pitch, but only suits fixed-design mass production.
Touch-screen substrate connections, RFID inlay chip bonding, EL backlight terminals, membrane switches, PC film substrates, irregular surfaces or local reinforcement, flip-chip FOB. The common thread: heat-sensitive substrates, irregular shapes, or modest volumes — on-site dispensing with ACP is more economical and flexible.
High-volume COG, COF, FOG and FOB display bonding — smartphones, OLED panels and automotive displays where precision is high, pads are small and pitches are dense. Take FOG (Film on Glass, an FPC bonded directly to glass): the ACF sits between the glass gold fingers and the FPC copper traces, and the joint is made in two stages — a low-temperature pre-press for alignment, then a high-temperature main press for curing.
The high-end ACF display market — smartphones, OLED, automotive, foldables — has long been led by two Japanese manufacturers, and both are the main benchmarks for domestic substitution:
| Brand | Background | Key products | Highlights |
|---|---|---|---|
| Dexerials | Tochigi, Japan; former Sony Chemicals + Toshiba Ceramics, merged in 2012 | PAF series, CP series, EH series | Ultra-fine pitch down to 15–20μm; COP and automotive-grade (IATF16949) qualifications |
| Resonac | Former Hitachi Chemical → Showa Denko Materials | ANISOLM brand, AC-3000 / AC-7000 / AC-10000 series | Pioneered practical ACF in 1984; particle-array types below 20μm, with contamination-resistant and reworkable grades |
These two essentially lock up the high-end ACF display segment; the narrow-width, reworkable ACF rolls commonly used in repair and rework also come mostly from their product lines.
1) Why repair cannot avoid ACF. A FOG/COF bond on a phone display is, in essence, "glass + ACF + FPC/IC". Replacing a flex cable, swapping a driver IC or repairing a broken trace all end with redoing an ACF bond — clean cutting, precise alignment and correct bonding parameters; miss any one and the job comes back. This is exactly why ZJWY builds its lamination and bonding equipment around alignment precision and controllable temperature/pressure.
2) Choosing material on the bench. Single-unit rework normally uses narrow-width, reworkable ACF (the small-roll grades from the two first-tier makers), sized to the display pitch: standard grades for regular FOG, particle-array fine-pitch grades for very dense layouts. Touch-screen and film repairs can use ACP applied on site. Avoid no-name bulk ACF — uneven particle distribution produces intermittent connections that are harder to debug than no repair at all.
3) Three bonding variables: temperature, pressure, time. ACF bonding is a two-stage process — pre-press for alignment, main press for curing. Too cool and the resin under-cures (open circuits after storage); too hot and the adhesive over-flows (bleed-out, shorts). Too little pressure starves particle capture; too much damages the glass. The stability and repeatability of your equipment’s parameters directly determine rework rates.
4) Acceptance criteria. After bonding, check three things: alignment — pad offset must stay within the pad width; appearance — no voids, no bleed-out, even particle distribution; electrical — stable loop resistance that does not drift after resting at room temperature. The most common "works sometimes, fails sometimes" complaint in the field usually traces back to insufficient particle capture or incomplete curing.