A kind of high vacuum pottery LCC method for packing
Technical field
The invention belongs to MEMS device packaging technique field, be specifically related to a kind of high vacuum pottery LCC method for packing.
Background technology
(Leadless Chip Carrier: leadless chip carrier) the high vacuum encapsulation technology is one of key technology of mode of resonance MEMS device to pottery LCC.Mode of resonance MEMS device to encapsulation require as follows: (1) requires high to the vacuum of encapsulation in the cavity, generally require less than 1Pa; (2) storage life limit for length, the general requirement is not less than 15 years.
Mode of resonance MEMS device encapsulation cavity is less, and to the discharge quantity and the venting rate of material in the chamber, and the sealing-in leak rate all proposed higher requirement, in addition, must use can carry out the getter that condition of high vacuum degree is kept in the encapsulation cavity.Because above-mentioned requirements, the key technology that relates generally to when pre-ceramic LCC high vacuum encapsulation technology and the problem of existence are as follows:
(1) mount technology.Promptly MEMS micro-structural chip attachment to the ceramic LCC pedestal, traditional pasting method has epoxy resin paster, elargol paster and silver-colored glass paster etc.The subject matter that the tradition pasting method exists is that paster material discharge quantity is bigger, can not satisfy the MEMS device in the encapsulation cavity less than the requirement of 1Pa.
(2) getter activation technique.Mode of resonance MEMS device can only be selected the higher nonevaporable getter of activationary temperature for use.Because the activationary temperature of the type getter is higher, thereby brought the problem of paster technique temperature and getter activationary temperature contradiction.Traditional getter Activiation method can not solve this temperature contradictory problems.
(3) sealing technology.Promptly around MEMS micro-structural chip, form a seal, to satisfy the needs of MEMS micro-structural chip to working environment.At present, generally adopt the eutectic technology to realize sealing-in, but all scolder eutectics all can produce the cavity, it is big to cause encapsulating leak rate, thereby causes the MEMS component failure.
The present invention has developed a kind of ceramic LCC high vacuum method for packing, can address the above problem.
Summary of the invention
The purpose of this invention is to provide a kind of MEMS device pottery LCC high vacuum method for packing, to solve the problem that exists in paster, sealing-in and getter activation technology link in the encapsulation of MEMS device pottery LCC high vacuum.
The technical solution adopted in the present invention is: a kind of high vacuum pottery LCC method for packing, and steps in sequence is as follows:
(1) treats encapsulating parts and carry out the plasma cleaning;
(2) eutectic paster, the micro-structural chip attachment to the ceramic LCC;
(3) pin interconnection is with being electrically connected of micro-structural chip and ceramic LCC;
(4) getter is activated;
(5) seal cover board and ceramic LCC are sealed in eutectic sealing-in.
The plasma cleaning method that step (1) is adopted is the radio frequency plasma cleaning method, the radio frequency plasma cleaning parameters difference of different parts, different with version and different according to the material of cleaning components, generally speaking, it is 100W-400W that plasma cleans power, and scavenging period is 2min-5min.
Step (2) eutectic paster step is:
A. micro-structural chip, paster scolder and ceramic LCC are placed on the paster special tooling, and in the patch device vacuum chamber of packing into;
B. the micro-structural chip is exerted pressure, and different, the paster region area is big more according to paster region area difference for this pressure size, and it is big more to exert pressure;
C. by carrying out temperature control curve the paster scolder is heated, concrete temperature control curve will decide according to the eutectic temperature point and the eutectic time of paster scolder, in addition, when being incubated, increased the pressure in the vacuum chamber after being heated to eutectic.
Step (3) adopts the WESTWOND7700E gold ball welding apparatus to carry out pin interconnection, finishes the welding of interconnected spun gold, and gold ball bonding connects parameter and will look concrete condition and determine, generally can be as follows: welding pressure 30gf, weld interval 200ms, bonding power 1.5W, 150 ℃ of welding temperatures.
Step (4) getter activates step:
A. encapsulating parts is put into vacuum chamber, encapsulating parts is carried out degasification, remove the gas of piece surface absorption;
B. select the consumption of getter for use according to concrete needs, packaging body is big more, and the getter consumption is big more, and it is long more that packaging body is preserved the time limit, and the getter consumption is big more; Determine activation parameter, activation parameter comprises 300 ℃-600 ℃ of activationary temperatures, activationary time 30min-60min and activates vacuum less than 10
-2Pa;
C. separate ceramic LCC base and the seal cover board that has getter, make seal cover board that has getter and the ceramic LCC base that has the sealing-in scolder lay respectively at high-temperature region and low-temperature space, the high-temperature region temperature is more than or equal to 500 ℃, and the low-temperature space temperature is smaller or equal to 200 ℃;
D. under the situation that activation environment vacuum meets the demands, carry out getter and activate temperature control curve.
Step (5) eutectic sealing-in step is:
A. after getter activated, used thermal insulation board when opening the getter activation combined ceramic LCC and seal cover board, and applies corresponding pressure, and different, the sealing region area is big more according to sealing region area difference for this pressure size, and it is big more to exert pressure;
B. carry out sealing-in scolder eutectic temperature control curve, finish the eutectic sealing-in, concrete temperature control curve will decide according to the eutectic temperature point and the eutectic time of sealing-in scolder.
Described a kind of high vacuum pottery LCC method for packing, paster scolder and sealing-in scolder are selected for use with a kind of scolder, for example golden tin solder, golden germanium scolder.
The invention has the beneficial effects as follows:
(1) by adopting the plasma cleaning method, improved package quality, reduced the whole leak rate of packaging body, problem promptly leaks outside;
(2) the present invention's method of selecting for use the eutectic solder identical with the sealing-in scolder to carry out eutectic is carried out paster, has reduced the discharge quantity of package interior material;
(3) activate by getter, can effectively adsorb a small amount of gas that discharges in the packaging body, guaranteed the better vacuum in the packaging body;
(4) the MEMS device that adopts high vacuum pottery LCC method for packing of the present invention to finish encapsulation satisfies following requirement: the vacuum in the encapsulation cavity is less than 1Pa, and the pot-life has realized that more than or equal to 15 years silicon micro-gyroscope Q value is about 150,000 encapsulation.
Description of drawings
The structural representation of Fig. 1 for adopting high vacuum pottery LCC method for packing of the present invention encapsulation to finish;
Fig. 2 is a high vacuum pottery LCC method for packing flow chart of the present invention;
Fig. 3 is golden tin solder temperature control curve schematic diagram;
Among the figure: 1, seal cover board; 2, sealing-in scolder; 3, ceramic LCC; 4, getter; 5, micro-structural chip; 6, interconnection spun gold; 7, paster scolder.
The specific embodiment
Below in conjunction with accompanying drawing the present invention is described in further detail.
The present invention will be packaged into this version shown in Figure 1 to each part shown in Fig. 1 by the described step of this method.
As shown in Figure 2, realize that concrete steps of the present invention are as follows successively:
(1) treat encapsulating parts and carry out the plasma cleaning: the part that cleans through ultrasonic wave comprises seal cover board 1, sealing-in scolder 2, and ceramic LCC 3, getter 4, paster scolder 7 adopts the radio frequency plasma cleaning technique again, and part is cleaned; The radio frequency plasma cleaning parameters difference of different parts, main different with version and different according to the material of cleaning components, generally speaking, it is 100W-400W that plasma cleans power, scavenging period is 2min-5min; Cleaning power as seal cover board 1 is 200W, scavenging period is 3min, it is 300W that sealing-in scolder 2 cleans power, and scavenging period is 4min, and it is 400W that ceramic LCC3 cleans power, scavenging period is 4min, it is 200W that getter 4 cleans power, and scavenging period is 3min, and it is 300W that paster scolder 7 cleans power, scavenging period is 3min, and cleaning gas is argon gas etc.Plasma cleans main advantage to be had: can clean the part of any material, can clean difform part, belong to dry method and clean, not have secondary pollution, obviously reduce the voidage of eutectic regions, thereby reduced the leak rate of sealing region.
(2) eutectic paster: promptly micro-structural chip 5 is mounted to ceramic LCC3.At first micro-structural chip 5, paster scolder 7 and ceramic LCC3 are placed on the paster special tooling, and in the patch device vacuum chamber of packing into; Then micro-structural chip 5 is applied certain pressure, and different, the paster region area is big more according to paster region area difference for this pressure size, and it is big more to exert pressure, and as the micro-structural chip 5 for 3mm*3mm, can adopt the pressure of 200g; At last, by carrying out temperature control curve (being that heating-up temperature is with changing the control curve heat time heating time) paster scolder 7 is heated, concrete temperature control curve will decide according to the eutectic temperature point and the eutectic time of paster scolder 7, be illustrated in figure 3 as golden tin solder temperature control curve schematic diagram, soaking zone 5min is the eutectic time, and 278 ℃ is eutectic temperature; In addition, when after being heated to eutectic, being incubated, increase pressure in the vacuum chamber to 100Pa-10000Pa, to reduce voidage by in vacuum chamber, charging into inert gas.By the above-mentioned steps operation, can obtain eutectic paster than good quality.
(3) pin interconnection: promptly realize being electrically connected of micro-structural chip 5 and ceramic LCC3, adopt the WESTWOND7700E gold ball welding apparatus to carry out pin interconnection, finish the welding of interconnected spun gold 6, gold ball bonding connects parameter and will look concrete condition and determine, generally can be as follows: welding pressure 30gf, weld interval 200ms, bonding power 1.5W, 150 ℃ of welding temperatures.
(4) getter is activated: at first encapsulating parts is put into vacuum chamber as shown in Figure 1, and encapsulating parts is carried out degasification, removes the gas of piece surface absorption; According to concrete needs,, select the consumption of getter 4 for use then as packaging body size, the preservation time limit etc., packaging body is big more, and getter 4 consumptions are big more, and it is long more that packaging body is preserved the time limit, consumption is big more, and for example the consumption of getter 4 is 3mm*3mm*10 μ m-10mm*10mm*100 μ m; Determine activation parameter, activation parameter comprises 300 ℃-600 ℃ of activationary temperatures, activationary time 30min-60min and activates vacuum less than 10
-2Pa etc.Concrete activation is as follows: at first, separate ceramic LCC3 base and the seal cover board 1 that has getter 4, make the seal cover board 1 that has getter 4 and lay respectively at high-temperature region and low-temperature space the ceramic LCC3 base that has sealing-in scolder 2, the high-temperature region temperature is more than or equal to 500 ℃, their are distinguished and guaranteed to the low-temperature space temperature by reliable clamping smaller or equal to 200 ℃ for two about for example with thermal insulation board vacuum chamber being divided into; Carrying out getter then under the situation that activation environment vacuum meets the demands and activate temperature control curve, is 500 ℃ as activationary temperature, and activationary time is 60min.In the getter activation, must guarantee that the low-temperature space temperature can not be too high, to avoid influencing sealing-in scolder 2 follow-up eutectic quality, for example for golden tin solder, the low-temperature space temperature can not be higher than 200 ℃.
(5) eutectic sealing-in: promptly seal cover board 1 is sealed with ceramic LCC3.After getter activates, used thermal insulation board when opening getter 4 activation, ceramic LCC3 and seal cover board 1 are combined, and apply corresponding pressure, and this pressure size is different and different according to the sealing region area, and the sealing region area is big more, it is big more to exert pressure, for example sealing region is circular, when the annulus area is 20mm2, can adopt the pressure of 400g; Carry out sealing-in scolder 2 eutectic temperature control curves then, finish the eutectic sealing-in, concrete temperature control curve will decide according to the eutectic temperature point and the eutectic time of sealing-in scolder 2.
Supplementary notes:
At the big problem of traditional paster material discharge quantity, the paster scolder 7 among the present invention is selected the eutectic solder identical with sealing-in scolder 2 for use, and optionally eutectic solder comprises golden tin solder, golden germanium scolder etc.The discharge quantity of eutectic solder will be much smaller than traditional paster material.There is the temperature contradictory problems in the eutectic pasting method of scolder of the same race, i.e. can destroy the eutectic patch layer of eutectic paster during eutectic sealing-in.Solved the temperature contradictory problems by the method for the invention, specific practice is as follows: at first, in eutectic paster process, parameter during by accurate control eutectic paster (eutectic temperature, eutectic time and exert pressure), the diffusion ratio of control eutectic patch interface Gold plated Layer gold atom, thereby the melting temperatur again (being that the eutectic patch layer is owing to being heated the temperature that melts once more) of control eutectic patch layer; Secondly, in eutectic sealing-in process, accurately control the parameter (eutectic temperature, eutectic time and exert pressure) of eutectic sealing-in, guarantee not destroy the eutectic patch layer.The degree of gold atom diffusion and to the strict degree of eutectic sealing-in quality requirement when the eutectic paster is depended in the requirement of accuracy of temperature control during the eutectic sealing-in.The control of melting temperatur again of eutectic patch layer is to guarantee follow-up eutectic sealing-in key of success.For example adopt golden tin solder, the melting temperatur again of scolder is controlled by the ratio of gold, tin in the eutectic patch layer, and gold content is high more, and melting temperatur is high more again.Ceramic LCC3 and the equal preplating of micro-structural chip 5 patch interface one deck gold, in eutectic paster process, the gold atom of Gold plated Layer is diffusion in the eutectic patch layer, thereby has improved the ratio of gold in the eutectic patch layer and then improved the melting temperatur again of eutectic patch layer.Control the melting temperatur again of eutectic patch layer by control Gold plated Layer gold atom toward the diffusion ratio in the eutectic patch layer, require the melting temperatur again of eutectic patch layer need be higher than 320 ℃ usually.