MIL- STD-883F 2004 TEST METHOD STANDARD MICROCIRCUITS - 第377页

MIL-STD-883F METHOD 2023.5 19 August 1994 5 3.2.1. 7 Proces s capab ility study . After t he wirebond pr ocess has been demons trat ed to be in a c ondition of stabi lit y and stat ist ical contr ol, a proc ess capabil i…

MIL-STD-883F

METHOD 2023.5

19 August 1994

3.2.1.2 Applicable manufacturing processes. Applicable manufacturing processes including bond pad metal disposition,

glassivation etch, and worst case package seal excursion shall have their critical characteristics determined and placed

under SPC control. Also, the process control requirements of the applicable general specification shall apply for these

operations including contamination controls, preventative maintenance procedures and schedules, and complete removal of

glassivation from the bonding pad.

3.2.1.3 For packages with gold plated posts

. For packages with gold plated posts, the device manufacturer shall perform

a bake test on one device from each incoming package lot. This test shall evaluate for basic plating or contamination

anomalies of the package post. The package shall be wire bonded post-to-post. The wire bonded package shall be baked

at 300 degrees celsius for 1 hour in either air or inert atmosphere. Bond strength shall then be tested in accordance with

MIL-STD-883, method 2011, using a sample size number = 45, C = 0 on the number of wires pulled. If any bond strength

failure is determined to be package plating or contamination related then the package lot shall not be used for this

alternative unless the defect can be effectively screened and the package lot resampled to a tightened sample size number

= 76, C = 0 for the number of wires pulled.

3.2.1.4 An active foreign material control program

. An active foreign material control program shall be in accordance with

MIL-STD-883, method 2010 or method 2017. A procedure and system for storing and handling wafers, packages, related

piece parts, and unsealed devices that will prevent contamination through package seal including face masks, lint free

gloves, restrictions on particle generating make-up, hair covers, and cleanroom gowns.

3.2.1.5 A 100 percent pre-bond visual inspection procedure

. A 100 percent pre-bond visual inspection procedure of the

die pads and package post shall be documented. The visual inspection shall be performed at 100-200X in a class 100

environment. Cleaning to remove rejectable contamination is allowed. No device shall exhibit evidence of the following

criteria:

a. Glassivation on the designed open contact area of the bond pads.

b. Chemical, film, photoresist or liquid contamination on the pads or posts.

c. Particulate and /or foreign material contamination on the pads or the critical bond area of the posts greater than

0.25 mils in diameter.

d. Die pads and package posts that do not meet all applicable requirements of MIL-STD-883, method 2010, condition

A or method 2017.

NOTE: 100 percent pre-bond visual inspection may be waived by the qualifying activity provided a 100 percent pre-

clean of pads and posts is performed, and all pads and posts for five (5) randomly selected devices pass the

inspection criteria. Precleaning may also be waived by the qualifying activity if historical data demonstrates the

cleaning is unnecessary. No cleaning is allowed during sample inspection. A 100 percent pre-clean and sample

inspection of 5(0) may be repeated a maximum of two times. Rejection of the sample after the second pre-clean

shall result in a 100 percent pre-bond inspection of the lot in accordance with 3.2.1.5. An investigation of the

rejects in the lot and sample shall be required and corrective action, as necessary shall be instituted. Until then,

100 percent pre-bond inspection is required. Once the effectiveness of any corrective action has been

determined, the 100 percent pre-bond inspection may be eliminated.

3.2.1.6 Bonding machine parameters

. Bonding machine parameters (e.g., temperatures, pressure, timing, fixtures, wire

size, wire material, height settings, etc.) must be defined for each die/package combination. The bonding equipment

parameters ranges shall be optimized by designed experiments. The experiments shall consider variations in bonding wire

geometry (e.g., loop height, wire length, shelf height, etc.). The experiments shall establish the predicted strength and

tolerance of the bonding operation. The allowable performance ranges of the bonding parameters determined by controlled

experiments shall be documented. Equipment parameter changes outside the allowable limits must be evaluated and

documented as to still meeting the predicted wire pull strength and tolerance.

Note: ASTM Standards F 458 and F 459 may be used as guideline documents.

MIL-STD-883F

METHOD 2023.5

19 August 1994

3.2.1.7 Process capability study. After the wirebond process has been demonstrated to be in a condition of stability and

statistical control, a process capability study shall demonstrate that the probability of any device failing the minimum

post-seal bond strength is P <.0001. The probability must meet the accumulative probability at the device level and not at

the individual wire level. The distributional form of the post-seal bond strengths shall be statistically evaluated for

conformance to the selected sampling distribution (e.g., Gaussian, lognormal, Wiebull, etc.). The capability study sample

size shall be sufficient to detect a shift in the distribution of the worst case package/die combination to a 100 parts per

million level. The beta risk to the consumer shall be .001 or less. (See Appendix A for normal distribution example.) The

process capability study shall be performed periodically. The capability study may be accomplished by characterizing the

wire pull strengths of one or more worst case package/die combinations. Selection of the worst case package/die

combinations should consider wire geometry, number of wires, pads and post sizes, etc. The characterization results from

worst case package/die combinations must be readily extended to all devices.

3.2.1.8 Control limits and action procedures

. The results of the evaluations in 3.2.1.6 and 3.2.1.7 shall be used in

determining control limits and action procedures for the wire bond operation. A destructive wire bond strength sampling plan

for each wire bonder shall include start and completion of each assembly lot, frequency of sampling the assembly lot, and

changes in operators (manual wire bonding only), wire spools, package lots, or setup conditions. The bond strength data

shall include the force required for failure, the physical location of failure, and the nature of the failure. Electrical rejects from

the same wafer lot may be used for the destructive wire bond pulls. In the event that bond wire strengths are outside the

predicted values for the wire, or class of wires with similar geometry, the bonder shall be inactivated immediately and not

returned to production until tests show that the operation is back under statistical control. A procedure for the traceability,

recovery, and disposition of all units bonded since the last successful bond strength test is required.

3.2.1.9 Time and temperature characterization

. Initially, a time and temperature characterization shall be performed for

each major type of wire bond metallurgical interface (e.g., gold/aluminum, etc.) to determine the electrical and mechanical

integrity of the wire bonds with respect to such factors as; flexing of wire bonds due to thermal expansion, and microcracks

or microvoids at the metallurgical interface. Evidence from the characterization shall demonstrate that the integrity of the

bonds is sufficient for a device to function over its expected life. Life usage conditions shall exceed 50,000 cycles from a 0 -

85 degree Celsius temperature range at the bonds. Time and temperature degradation factors for accelerated testing must

be justified against these minimal life usage conditions.

3.2.1.10 Wire bond integrity

. If pre-burn-in, interim and post burn-in electrical failures (opens/shorts), qualification, or

quality conformance inspection failures indicate questionable wire bond integrity then an analysis is required to verify the

bond integrity. If any bond is confirmed to be defective; the applicable inspection lot or sublot will be rejected, an evaluation

performed to determine the cause of the bond failure, corrective actions implemented based on the evaluation, and

disposition of other affected inspection lots or sublots. The failure analysis and corrective actions will be retained and made

available to the qualifying activity upon request.

MIL-STD-883F

METHOD 2023.5

19 August 1994

3.2.2 Lot acceptance procedure. Each assembly lot shall receive a post-seal bond wire integrity acceptance test. A

separate assembly lot acceptance test is required for each wire bonder, and for any changes in setup conditions, wire spool,

package lot, or wafer lot, unless such differences have been demonstrated to be statistically insignificant. A post-seal

destructive wire bond sampling and test plan with the following minimum requirements shall be documented.

a. More than one device shall be subjected to the acceptance test. Electrical, non-wire bond related visual, or

package seal rejects may be used for the post-seal wire bond test.

b. The destructive wire pulls shall be evaluated in meeting the post-seal bond strength limits in MIL-STD-883, Method

2011, or as established in 3.2.1.7. The assembly lot shall be accepted if the wire bond strengths meet the

requirements of sections c, d, and e below.

c. All wires or a minimum of 50 randomly selected wires shall be pulled from each sampled device. The post-seal

bond strength distribution(s) must demonstrate that the wire bond process is in statistical control, has not changed

with respect to the distribution characterized for a one-sided lower control limit, and no single destructive pull is

less than the specified post-seal bond strength limit. The sample size shall be sufficient to demonstrate that the

statistical distribution of all wires pulled has not changed with respect to central tendency or dispersion in such a

way as to violate a p < .0001 at the device level. The beta risk to the consumer shall be .01 or less. The method of

statistical analysis shall be documented and approved by the qualifying activity.

d. A minimum of 8 wires shall be evaluated from each sampled device to represent the worst case wires as

determined to potentially violate the lower specification limit. Their wire pull strengths shall be within the predicted

tolerances established in 3.2.1.6. Any wire pull strengths outside the predicted tolerance in the characterized

distribution shall require evaluation as to the cause of the out of control condition, and additional worst case wires

shall be pulled to determine whether the wire bond strength distribution meets a probability at the wire level of

P < 1-[.9999**(1/n)] (n = number of bonding wires in the package). The lot is rejected if this criteria is not met.

e. If any bond fails the acceptance criteria, a documented action plan shall be followed to determine the cause of the

failure. Wire bond failures verified as non-bond related shall be documented, and additional post-seal wire bond

pulls shall be conducted to demonstrate statistical control as described in 3.2.2.1.c and d. If a failure is verified as

bond integrity related (e.g., contamination on wire, glassivation on the bonding pad, etc.), all devices within the

applicable assembly lot shall be rejected. Wire bonding shall be suspended on the applicable bonding equipment

until a failure analysis, MIL-STD-883, method 5003, of the failed bond is performed and corrective action is

implemented and recorded.

4. SUMMARY

. The following details shall be specified in the applicable acquisition document:

a. The applied lifting force if other than as specified in 3.1.

b. The sampling, acceptance, or screening requirements.

c. The percent defective allowable (PDA) as applied to the number of failures with respect to the number of wires

tested.

d. The requirements for reporting of failure categories, when applicable.