Development of high-overload LTCC integrated LCC package.
He Zhongwei, Li Jie, Zhou Donglian, He Biao, Lu Daowan.
North General Electronics Group *** Microelectronics Department).
Abstract:Through the research on the design of the packaging structure and its manufacturing process, the manufacturing process of LTCC substrate processing, eutectic welding of frame and substrate, parallel seam welding and capping, etc., the LTCC integrated LCC package shell suitable for multi-chip and multi-device microelectronic modules has been successfully developed, and the airtightness of the package meets the requirements of the first standard, and can reach the high overload level of 25000 g mechanical impact stress.
LCC (leadless chip carrier) is a surface-mount package enclosure with metal film terminals instead of metal leads [1,2], which is basically made of multilayer HTCC (high-temperature co-fired ceramic) with a mass fraction of 90% 96% Al 2 O 3, and the interconnecting conductors are refractory metals such as W (tungsten) and MO (molybdenum), and the sintering is completed at a high temperature of 1 500 1 800 and in a reducing atmosphere. After plating Ni (nickel) or Ni and Au (gold) on the surface of W or Mo conductor layer, the chip and sealing ring installation area, the interconnection bonding area and the package terminal area are formed, and the installation of the metal sealing ring is realized by more than 600 high-temperature brazing (such as silver brazing) process. HTCC LCC is a ceramic hermetic package, which has excellent thermal performance, mechanical strength, and resistance to harsh environments, but has the disadvantages of poor conductivity of interconnected conductors, complex process, high process temperature, inability to print resistors, and the need for coating processing [3], and can generally only be used to package a single large-scale monolithic IC (integrated circuit) chip.
The integrated LCC package interconnect based on LTCC (low-temperature co-fired ceramics) has short lines, small parasitic parameters, excellent dielectric properties, dense package terminals, good machinability, and easy cavity, which is very suitable for packaging microelectronic module products such as MCM (multi-chip components), MEMS (microelectromechanical system) integrated components, and high-frequency microwave integrated components composed of multiple IC chips and various electronic components (semiconductor devices, chip resistor-capacitance components, sensors, etc.) [4,5].
In this paper, a castle-style miniaturized LCC package integrated with high-density interconnect LTCC substrate is developed, which can be used to package microelectronic modules with multi-chip and multi-device devices, and can meet the high overload resistance requirements of 25000 g (g is gravitational acceleration) impact acceleration.
1. Package structure design.
The structural design of the LTCC integrated castle LCC package is as follows.
1) The three basic parts that make up the "LTCC integrated castle LCC package" are "LTCC substrate with cavity" (as shown in Figure 1), "metal frame" and "metal cover", "metal frame" and "LTCC substrate with cavity" are eutectic welded to form an "integrated LCC package shell" (as shown in Figure 2), and the "metal cover" is welded parallel seam on the "integrated LCC package shell" to form the whole package (as shown in Figure 3);
2) The area size A B 15 mm 15 mm and the thickness of the cavity base plate are 1 mm, and the pitch E 1 is made of the substrateThe 27 mm (or 1 mm) bottom surface leads to a metal coating (0. wide5 e ～0.7 e, length is e).
Semi-cylindrical holes with surrounding sidewalls (height 0.).67 t and radius r 02 e ～0.3 e, t is the thickness of the substrate) the castle-shaped SMT solder area terminal composed of the metal film layer, the four corners of the substrate are chamfered at 1 mm 45°, one or more square semi-through cavities in the substrate are used to install chips and other components with larger thickness, the LTCC substrate of multi-layer electrical interconnection is made of LTCC raw porcelain tape and its supporting hole filling and screen printing electronic paste, and the bottom surface of the substrate and the side wall of the castle-shaped terminal film layer and the top surface of the annular eutectic welding bead film layer (width is 1.).2 w ～1.5 W, W is the wall thickness of the metal enclosure) is made of thick film PDAG (palladium-silver) conductor slurry;
3) The height of the square frame shape "metal enclosure" with four corners rounded is 05～2.0 mm, wall thickness 08～1.0 mm, made of 4J29 Kovar alloy, Ni AU plated on the surface;
4) The thickness of the seam welded frame shape edge around the four corners of the rounded sheet "metal cover plate" is 01 mm, thickness 0 in the middle area25 mm, made of 4J29 Kovar alloy with Ni Au plating.
2 Package manufacturing process.
2.1 Manufacturing process.
The brief process flow of LTCC integrated castle LCC package manufacturing is as follows: "LTCC substrate with cavity" processing, metal film layer fabrication of semi-cylindrical hole castle-shaped terminals on the side wall around the metal film "metal frame" and "LTCC substrate with cavity" eutectic welding (after the assembly of components in the package) parallel seam welding "metal cover" and "integrated LCC package housing".
2.2 LTCC substrate processing.
Fabrication of small-size LTCC substrates with cavities with castle-shaped half-pass half-cylindrical hole SMT terminals on four sidewalls, and multi-chip processing according to the basic LTCC process.
1) The model and size of the qualified LTCC porcelain piece perforated, each raw porcelain piece punched through hole including the middle of the corresponding layer of interconnection holes to be filled and the four corners (edge) area of the hole filling is not filled with alignment group holes, laminated with positioning group holes, substrate four corner area 1 mm 45 ° chamfered piece synthesis 141 mm×1.41 mm square hole and substrate lower 067 times the thickness of the side wall castle-shaped semi-cylindrical hole of each layer of porcelain layer on the piece to form a round hole;
2) through the hole filling on each piece of raw porcelain sheet screen printing with alignment group hole alignment, with AG hole filling conductor slurry layer by layer to complete the raw porcelain piece through hole filling and drying;
3) through the filling of holes on each piece of raw porcelain sheet, the screen printing is aligned with the alignment group hole, and the conductive tape printing and drying of the raw porcelain piece are completed layer by layer with the screen printing conductor slurry;
4) Using a laser dicing machine, the raw porcelain window is cut on each raw porcelain layer of the LTCC cavity in the upper part of the substrate;
5) Layer by layer, hang the four corners of the raw porcelain piece on the corresponding pin of the stacking table, and stack it into a loose whole piece of raw porcelain billet;
6) Fill the cavity of the upper part of the whole raw porcelain blank with the cavity plug with the correct shape and size, cover the metal pressing plate, vacuum seal it with a plastic bag, and place it with a pressure greater than 20The aqueous medium of 265 MPa and the temperature of 70 was laminated under medium static pressure for 10 min.
7) Using a raw porcelain hot cutting machine, the whole piece of raw porcelain plate is cut into a unit substrate raw porcelain block according to the alignment of the cutting mark line on the surface of the compacted raw porcelain plate, and the cylindrical hole of each whole plate of the joint piece is cut into a castle-like semi-cylindrical hole on the side wall around the raw porcelain block of each unit substrate;
8) Using the LTCC sintering furnace, the raw porcelain blocks of each unit substrate are fired into the unit LTCC substrate;
9) Thick film screen printing, drying, and sintering processes are used to complete the production of the PDAG film layer of the square frame eutectic weld bead on the top surface of the LTCC substrate and the SMT terminal on the bottom side;
10) Adopt the manual coating method to complete the side printing of the castle-shaped semi-cylindrical hole terminal film layer on the side wall of the substrate.
2.3. Eutectic welding of the frame and substrate.
A vacuum eutectic furnace is used to complete the eutectic welding of the metal frame on the top surface of the LTCC substrate.
1) Clean the metal frame and LTCC substrate, remove surface pollution, and dry;
2) Set the temperature curve and vacuum-nitrogen-formic acid atmosphere curve of eutectic furnace welding, with a maximum welding temperature of 320 330 and a peak temperature of 3 5 min;
3) Will be thick 0The 05 mm AU80SN20 alloy solder sheet is cut to the same shape and size as the eutectic bead layer on the top surface of the LTCC substrate.
4) On the surface of the welding platform of the eutectic furnace, the LTCC substrate (cavity side facing up), the box-shaped AU80SN20 alloy solder sheet and the Kovar alloy frame are stacked and placed in turn, so that the eutectic soldering bead film layer, solder sheet and the frame are aligned and pressed on the top surface of the frame with a ceramic block of appropriate quality;
5) Open the eutectic furnace, complete the eutectic welding according to the set welding temperature curve and welding atmosphere curve, and obtain the "integrated LCC package shell" component.
2.4 Parallel seam weld caps.
Parallel seam welding is performed after the assembly of internal components such as IC chips and MEMS sensor chips is completed.
1) Scrub the metal cover plate and LCC package shell, remove the contamination on the cover interface, and dry;
2) Put the LCC package shell (including internal components) and the metal cover plate into the vacuum oven of the parallel seam welding system, and bake in a hot vacuum environment for 4 8 h;
3) Arrange the parallel seam welding program, and set the welding parameters such as seam welding current, running speed, running distance and electrode pressure;
4) Put the LCC encapsulated shell into the welding fixture on the workbench of the parallel seam welding machine, place and align the metal cover plate according to the orientation requirements;
5) Start the seam welding process, and melt and seal the metal cover plate and metal frame in the nitrogen-filled operation box of the parallel seam welding system to achieve the airtightness of "LTCC integrated castle LCC package".
The sample substrate, housing, and entire piece of the LTCC integrated LCC package are shown on the left, middle, and right in Figure 4, respectively.
3. Seal tightness test.
Press GJB548B-2005 "Method 1042".2. Condition A1 in "sealing" requires that the tracer gas helium (HE) fine leak detection test of 9 uncapped "integrated LCC package shell" samples was completed, and all of them were qualified, and the measured leak rate was 80×10 －5 ～1.2×10 －4 pa·cm 3 /s（he）。
According to GJB548B-2005 method 10422. Condition A1 and Condition C1 require that the fine leak detection test and fluorocarbon crude leak detection test of the "LTCC integrated LCC package shell" samples after 9 caps are completed, and the measured leak rate is (1.).5～2.3）×10 －3pa·cm 3 /s(he)。
4. High overload assessment test of package resistance.
Nine samples of the uncapped "integrated LCC package shell" and the parallel seam welded cap "LTCC integrated LCC package shell" were used as test objects, and the GJB548B-2005 "method 20021 Mechanical Shock" test, which assesses the high level of overload stress of this package.
1) The design and processing of the impact test fixture should mainly ensure that the sample is effectively clamped, so that it can withstand the mechanical impact stress set by the test without being subjected to the excess destructive force exerted by other components. The length and width of each groove are the same as the length and width of the sample and the depth is slightly larger than the thickness of the sample, so that the sample can just be loaded into the groove with a layer of filter paper at the bottom and not higher than the upper surface of the groove, and the aluminum alloy beading is fixed with an aluminum alloy bead after one to two layers of filter paper are padd on the top surface of the sample, and then the sub-fixture is fixed on the bearing surface of the impact table for impact test. It can ensure that the inertia force generated by the beading during the impact test acts on the surface of the sub-fixture and will not act directly on the sample rigidly, so that the test results can truly reflect the mechanical impact stress level of the sample;
2) The mechanical impact directions are y 1, y 2, x and z respectively (as shown in Figure 6);
3) The mechanical impact stress is in order: 2000 g 03 ms，3000 g /0.3 ms，5000 g /0.3 ms，8000 g /0.2 ms，10000 g /0.2 ms，15000 g /0.1 ms，20000 g /0.1 ms，25000 g /0.1 ms；
4) 5 impacts of each stress in each direction, and visual inspection under a stereo microscope with 20 times magnification after each impact test is completed, and the sample should not be deformed, cracked and other mechanical damage;
5) if there is no abnormality in visual inspection, then pass the impact test of this stress in this direction, and this sample continues to carry out the test of next stress in the next direction; If the visual inspection is unqualified, the failure phenomenon will be summarized, the cause of the failure will be analyzed, and the follow-up test of the sample will be stopped.
The test results showed that all 18 samples could pass the mechanical impact stress test with acceleration of 2000 g and 20000 g each time (5 times each) in the four directions of y 1, y 2, x and z. The Y 1 direction (i.e., the weakest direction of the mechanical strength of the sample's impact resistance - the direction of the thickness of the cavity and bottom plate in the LTCC substrate) and the acceleration of 25000 g of the two types of samples can also pass the impact test normally.
5 Conclusion. Based on the above development, it can be seen that:
1) The "LTCC integrated LCC package" based on LTCC multilayer substrate and integrated packaging technology has the characteristics of compact structure, excellent performance, high reliability and wide range of applications.
2) The LTCC substrate processing, eutectic welding of frame and substrate, parallel seam welding and capping involved in "LTCC integrated LCC packaging" are mature and operable;
3) The hermetically tightness of "LTCC integrated LCC package" meets the requirements of GJB548B-2005, which can meet the long-term hermetic packaging protection requirements of MEMS, MCM and other devices and components;
4) The miniaturized "LTCC integrated LCC package" housing and its basic component "integrated LCC package housing" can achieve a high overload level of 25,000 g mechanical impact stress.