Patent Description:
One example method of delidding an IC package is by grinding and/or polishing away the lid to expose the cavity in the ceramic body containing the die, ball bonds, and bond wires. Another example method is using acid etching. However, IC packages can contain delicate hardware, such as the die, ball bonds, and bond wires. Some methods of delidding an IC package can damage this delicate hardware, and can be excessively time consuming.

<CIT> relates to a method of hermetically laser sealing electronic packages and discloses a method of delidding an integrated circuit (IC) package, comprising: milling, peeling off and fly cutting a cut line of an integrated circuit package, the cut line defining a removable portion; cutting along the cut line; and removing the removable portion; wherein the integrated circuit package includes a body and a lid, the lid defining a hermetically sealed cavity therein, wherein the lid includes a side wall extending from the body to a top surface of the lid, and wherein the removable portion includes the top surface of the lid.

<CIT>, <CIT> and <CIT> relate to methods of delidding molded packages, wherein delidding is carried out by laser beam ablation.

The inventive method of delidding an integrated circuit (IC) package is defined in appended claim <NUM>. The dependent claims are directed to preferred embodiments of the invention.

<FIG> show an example integrated circuit ("IC") package <NUM>. The IC package <NUM> includes a body portion <NUM>. The body portion <NUM> includes a cavity <NUM> and a lid <NUM> that covers the cavity <NUM>. Accordingly, the example IC package <NUM> of <FIG> are known as "cavity ICs. " The IC package <NUM> includes one or more device pins <NUM> (<FIG>) for connecting the IC package <NUM> to a printed wiring board (PWB) (not shown).

In one example, the IC package <NUM> is a dual in-line package (DIP).

The lid <NUM> includes a top surface 14a and side walls 14b. In some examples, the lid <NUM> also includes a foot portion 14c that extends out from the side walls 14b along some extend of the body portion <NUM>. The cavity <NUM> is hermetically sealed by the lid <NUM>. In one example, the lid <NUM> is attached to the portion <NUM> at the foot section 14c. In another example, the foot section 14c is omitted, and the lid <NUM> is attached to the body portion <NUM> along a perimeter of the side walls 14b.

In some examples, the body portion <NUM> of the IC package <NUM> comprises a ceramic-based material, and the lid <NUM> comprises a metallic-based material, such as lead, tin, or a mixture thereof. The attachment of the lid <NUM> and body portion <NUM> discussed above can be any suitable attachment method for the respective materials that enables a hermetic seal, such as welding, brazing, gluing, or other methods.

In the example shown, the lid <NUM> is generally rectangular, though other shapes are contemplated.

<FIG> shows an example IC package <NUM> that is "delidded," e.g., the lid <NUM> has been removed. As shown, the IC package <NUM> contains circuitry <NUM> situated in the cavity <NUM>, including in some examples a die, ball bonds and bond wires, or other features as would be known in the art. The circuitry <NUM> enables the IC package <NUM> to perform a computing function for the PWB as would be known in the art. In one example, the PWB is included in a device of a gas turbine engine.

Occasionally, an IC package <NUM> is delidded in order to gain access to the circuitry <NUM> therein. For example, the IC package <NUM> may exhibit a malfunction. Root cause analysis and troubleshooting the malfunction may require physical access to the circuit <NUM> in order to study its individual components and identify malfunctions thereof. For instance, troubleshooting may include visually (or microscopically) inspecting the circuitry <NUM> for signs of burning, electrical overstress, broken/disconnected parts, or other issues.

The inventive way to delid an IC package <NUM> is to laser-cut the lid <NUM> so that it can be removed. <FIG> shows an example laser apparatus <NUM> for laser-cutting the lid <NUM>. The example laser apparatus <NUM> includes a laser source <NUM>, a scan head <NUM>, and a laser stage <NUM>. In one example, the laser source <NUM> is a femtosecond laser source <NUM>, which emits optical pulses with a duration on the order of femtoseconds. In a more particular example, the laser is a <NUM> femtosecond laser source <NUM>, e.g., it emits optical pulses with a duration of <NUM> femtoseconds. The laser source <NUM> can be operated in a burst mode, in one example. In the burst mode, an output from the laser source <NUM> is limited by the heat capacity of the laser medium. The laser source <NUM> operates until the medium reaches a maximum acceptable temperature ("burst" or "pulse"), then shuts off and is cooled before repeating the burst. In a particular example, the energy per burst of a laser beam L produced by the laser source is between about <NUM> and <NUM> micro Jules. In a more particular example, the energy per burst is about <NUM> micro Jules. In one example, the rate of the bursts is <NUM>.

One or more beam expanders <NUM> are situated between the laser source <NUM> and scan head <NUM> to expand the size of the beam L from the laser <NUM> according to any known method and associated apparatus. One or more mirrors <NUM>, such as galvo-mirrors, are situated in the scan head <NUM>. The mirrors <NUM> are positioned on pivots <NUM> so that the mirrors <NUM> are rotatable. The mirrors <NUM> direct the beam L to a lens <NUM>, such as an f-theta lens. The lens <NUM> directs the laser beam L to a component in the laser stage <NUM>. In this example, the component is an IC package <NUM>.

In one example, the laser apparatus <NUM> includes a controller <NUM> that is operable to control one or more of the laser source <NUM>, the scan head <NUM>, the beam expanders <NUM>, and the pivots <NUM> as would be known in the art.

In some examples, the laser apparatus <NUM> includes an air flow generator such as a fan (not shown) to further remove any heat generated during the process.

In accordance with the claimed invention a method <NUM> of delidding an IC package <NUM> by laser cutting is shown in <FIG>.

In step <NUM>, an IC package <NUM> is placed in a laser apparatus <NUM>, and in particular in a laser stage <NUM> of the apparatus <NUM>.

In step <NUM>, the laser is directed along a cut line of the IC package <NUM> by the mirrors <NUM> and lens <NUM> as discussed above. The cut line C defines a removable portion R of the IC package <NUM>. Cutting along the cut line C defines a cut surface. <FIG> show example cut lines C. In <FIG>, cut line C is through the side wall 14b of the lid <NUM> and around the perimeter of the lid <NUM>, e.g., the cutting defines a cut surface that is is generally parallel to the body portion <NUM>. In this example "generally parallel" includes a slight angle of about <NUM> degrees or less with respect to the body portion <NUM>. In this example, the removable portion R includes the top surface 14a of the lid <NUM>. In <FIG>, the cut line C is along the foot portion 14c of the lid <NUM> around the perimeter of the lid <NUM>, e.g., cutting along the cut line C defines a cut surface that is perpendicular to the body portion <NUM>. In this example, the removable portion R includes the entire lid <NUM>, including the side walls 14b. The cut line C may be selected depending on the attachment of the lid <NUM> to the body portion <NUM>, discussed above. In one example, the laser beam L is directed along the cut line C at an angle that is perpendicular to the cut line C, though other angles may be contemplated.

The directing includes scanning the laser beam L along the cut line. As is schematically shown in <FIG>, the laser beam L produces a circular spot S with a radius r. The spot size S is related to the radius of the laser beam L at the laser source <NUM>, and the focal length, which is related to working distance for the laser apparatus <NUM> (the distance between the scan head <NUM> and the laser stage <NUM>). Also the greater the working distance, the larger the radius r of the spot S. In one example, the radius r is between about <NUM> and <NUM> microns and the working distance is between about <NUM> and <NUM>. In a particular example, the radius r is about <NUM> microns and the working distance is about <NUM>.

For example, <FIG> shows four spots S. "Scanning" includes producing these successive spots S along the cut line C. The successive spots S overlap by an overlap O. In one example, the overlap between spots S is between about <NUM> and <NUM> % of the size of the spots S, which is known as a "pulse overlap. " In a more particular example, the pulse overlap is <NUM>%. In one example, a distance d between center points of successive spots S is about <NUM>, which is known as "line distance. " The pulse overlap and line distance are related to an "overlap per line" which corresponds to an effective amount of overlap along the length of the cut line C caused by the scanning. In one example, the overlap per line is between about <NUM>% and <NUM>%. In a more particular example, the overlap per line is about <NUM>%.

In one example, the directing may include (in addition to the scanning) rotating or moving the IC package <NUM> on the laser stage <NUM>. In another example, the directing includes rotating or moving the laser stage <NUM>, and the IC package <NUM> remains stationary on the laser stage <NUM>. In another example, the directing only includes directing the laser beam L by the mirrors <NUM> and lens <NUM>, and the IC package <NUM> and laser stage <NUM> remain stationary. Any combination of these examples is also contemplated, e.g., rotating/moving the IC package <NUM> and/or the laser stage <NUM> and/or directing the laser <NUM> by the lens <NUM>. The directing can be controlled by controller <NUM> in some examples.

In step <NUM>, the removable portion defined by the cut line C is removed from the IC package <NUM>.

The laser cutting according to the method <NUM> described above results in a clean, defined cut edge that minimally disrupts surrounding material of the body portion <NUM>. The minimal disruption includes minimal heat dissipation from the laser beam L to material of the body portion <NUM> surrounding the cut line C. <FIG> show scanning electron microscope images of an example body portion <NUM> before laser cutting according to the method discussed above (<FIG>) and after laser cutting according to the method discussed above (<FIG> is more magnified than <FIG>. As shown, the material of the body portion <NUM> exhibits minimal disruption after cutting according to the method <NUM> described above.

Because the laser cutting according to the method <NUM> has such minimal disruption to surrounding material and since the circuitry <NUM> is in a cavity untouched by the laser beam, the circuitry <NUM> is minimally damaged or changed by the laser cutting. Accordingly, the circuitry <NUM> remains in substantially the same state as before the delidding even after the delidding. Therefore, in the case of IC package <NUM> malfunction, the circuitry <NUM> can be observed in substantially the same state in which it malfunctioned, better enabling determination of the reason for malfunction and root cause analysis. On the other hand, other methods of delidding, such as grinding away the lid <NUM> or cutting the lid <NUM> with a mechanical tool such as a razor blade are exceedingly time consuming and may cause damage to or change the circuit <NUM> in the process of delidding.

Additionally, the laser cutting according to the method <NUM> is relatively fast. In one example, an IC package <NUM> can be delidded on the order of minutes, for instance <NUM> minutes. On the other hand, the other example methods of grinding or cutting with a mechanical tool can take several hours.

Claim 1:
A method of delidding an integrated circuit, IC, package, comprising:
directing (<NUM>) a laser beam (L) along a cut line (C) of an integrated circuit package (<NUM>), the cut line defining a removable portion (R);
cutting along the cut line; and
removing (<NUM>) the removable portion after the directing;
wherein the integrated circuit package includes a body portion (<NUM>) and a lid (<NUM>), the lid defining a hermetically sealed cavity (<NUM>) therein, and wherein the lid includes a side wall (14b) extending from the body portion (<NUM>) to a top surface (14a) of the lid, and wherein the removable portion includes the top surface of the lid.