How prevent reload entire page using __doPostBack?

Question

I am using a aspx page and inside a modal window i make __doPostBack, but this causes the entire page is reloaded.

I tried with:

1. __doPostBack('<%= btn_search.UniqueID %>', "")
2. __doPostBack('<%= btn_search.ClientID %>', 'OnClick')
3. $('btn_search').trigger('click');

also i tried with a hidden button : __doPostBack('ctl00$ContentPlaceHolder1$btn_search','')

but the result its the same, all page is reloaded.

how can i prevent reload the entire page ?

    bootbox.dialog({
    title: "Validacion Paciente",
    message: "<input type='text' id='mensaje' class='border border-white' name='mensaje' style='display: none;'/><div id='content-capture' style='display: none;'> <div id='status'></div> <div id='imagediv' class='mb-2'></div> </div> <div id='Scores'>  <input type='hidden' id='qualityInputBox' size='10' style='background-color: #DCDCDC; text-align: center;'> </div>",        
    buttons: {
        main: {
            label: "Continuar",
            className: "btn-primary",
            callback: function () {

                __doPostBack('<%=  btn_search.ClientID %>', 'OnClick');                    


            }
        }
    }
});