try using something like this.
https://www.ebay.com.au/itm/1PC-ACF-conductive-film-large-size-TAB-rework-conductive-adhesive-AC-7206u-18/273898017985?hash=item3fc59814c1:m:mKs9phkl09QEEGAwkT_Zyqw
You will need a localized heat press to activate it but it is what they used initially I think.