How to post back on button click which is present in second overlay

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C#

C#4.0

We have 2 overlay , the first overlay (hdOverlay) is displayed ondouble click of row(from javascript), and second overlay is displayed on click of button(btnViewDeals) present in first overlay(from code behind), till this process we get IsPostBack true (i.e., page is postback), but on click of button(btn1) present in second overlay page is reloading(i.e., IsPostBack is false )and not going to button click event.Please anyone help i want IsPostback true and proceed furthur .Thanks in advance

<div id="hdOverlay" style="display: none; removed: absolute; border: 1px; background-color: #fffff0;border-removed #000000 1px solid; border-removed #000000 1px solid;<br mode=" hold=" />        border-right: #000000 1px solid; border-top: #000000 1px solid;width: 700px;">
        <form id="hdDealForm" action="">
<table width="100%">
            <tr>
                <td align="left">
<asp:Button ID="btnViewDeals" runat="server" CssClass="formButton" Text="View Deals" OnClick="btnViewDeals_Click" />
 </td>
</tr>
</table>
</form>
    </div>

<div id="hdoverlayDealDetails"  runat="server" style="display: none; position: absolute;
        top: 100px; left: 100px;">
        <form id="hdDealDetails" action="" style="width: 80%; margin: 0 auto; padding: 5px;
        background-color: #fffff0; border: solid 1px #000000; z-index: 2">
        <table width="100%">
            <tr>
                <td>
<asp:Button ID="btn1" Text="Export" CssClass="formButton" runat="server"
                        Visible="false" OnClick="btn1_Click" />
 </td>
            </tr>
</table>
</form>