Solder mask inkjet inks for manufacturing printed circuit boards

A radiation curable solder mask inkjet ink comprising:

• a photoinitiator;
• a free radical polymerizable compound;
• and
• an adhesion promoter;
• wherein
• the adhesion promoter has a chemical structure according to Formula I:
• wherein
• R1 is selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl or heteroaryl group, OR5, SR6, and NR7R8;
• R2 is selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, and a substituted or unsubstituted aryl or heteroaryl group;
• R3 is selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl or heteroaryl group, and an electron withdrawing group including at least one oxygen carbon double bond or a nitrile group;
• R2 and R3 may represent atoms that form a 5 to 8 membered ring;
• R4 is selected from the group consisting of an electron withdrawing group including at least one oxygen carbon double bond or a nitrile group, and a substituted or unsubstituted aryl or heteroaryl group;
• R5 and R6 are independently selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, and a substituted or unsubstituted aryl or heteroaryl group;
• R7 and R8 are independently selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, and a substituted or unsubstituted aryl or heteroaryl group;
• R7 and R8 may represent atoms that form a 5 to 8 membered ring;
• and
• none of R1 to R4 includes a photoinitiating moiety.