GB2475600A

GB2475600A - Synchronous testing of the solderability of components and solder paste usability

Info

Publication number: GB2475600A
Application number: GB1018958A
Authority: GB
Inventors: Graham Naisbitt
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-11-21
Filing date: 2010-11-10
Publication date: 2011-05-25
Also published as: GB0920488D0; GB201018958D0; GB201017170D0; GB201009682D0

Abstract

The ability of a solder paste 3 to wet onto an electrical component 1 terminal is tested using apparatus comprising heated bath 4, mini-crucible 8, test jig plate 2, lift mechanism 5, load sensor 10, and control module 11-13. The control module causes the lift mechanism to raise the heating bath into contact with the test jig plate that in turn rises so as to bring the component into contact with the solder paste in the test jig plate. The load sensor then measures the force arising from wetting of the solder paste to the contact surface. The force generated under contact changes over time depending on the degree of solderability of the component. Measurement of the wetting forces over time provides an indication of both the wetting ability of the solder paste and the solderability of the component.

Description

Description:

Embodiments described herein relate generally to methods and apparatus for use in determining the solderability of an electrical component (see figure 1:1).

This generally comprises a load sensor (see figure 1:10), a heated bath (see figure 1:4), a base platform (see figure 1:6) and a control module (see figure 1:11,12,13). The controller raises the heated bath from the base platform (see figure 1:6) so that the electrical component is brought into contact with the load sensor. When the contact portion is brought into contact with the molten solder in the heated bath, the load sensor measures force arising from wetting of the solder to the contact surface. The force occurring under contact changes over time depending upon the degree of solderability of the electrical component. The force is able to be measured in mN.

The problem relates to the use of a solder paste (see figure 1:3), rather than pure solder, to measure both the ability of the solder paste to wet onto the contact surface, as a measure of its usability, and of the solderability of the electrical component.

Another problem relates to the solder paste that comprises a powdered metal alloy and a flux. When the solder paste is heated to its melting point, the flux will boil vigorously so that conventional apparatus would be unable to achieve an accurate force measurement and hence the usability of the paste and the solderability of the electrical component.

To overcome these problems we have developed apparatus comprising a heated bath and integral mini-crucible (see figure 1:8), a Test Jig Plate (see figure 1:2) and a set of adjustable sprung bars (see figure 1:9), all of which are then attached to a lift mechanism (see figure 1:5), a load sensor (see figure 1:10), a base platform and a control module. This assemblage is then brought into use in a synchronous manner.

The control module causes the lift mechanism to synchronously, raise the heating bath mounted on the platform into contact with the Test Jig Plate that is in turn put into contact with the sprung bars. This then creates sufficient time to allow for the volatilisation of the solder paste flux so that it does not detrimentally affect the force measurement. The assembly continues to rise so as to then bring the electrical component into contact with the now molten solder paste in the Test Jig Plate. The load sensor then measures the force arising from wetting of the solder paste to the contact surface.

The force generated under contact changes over time depending on the degree of solderability of the electrical component (Figure 5). Thus measurement of the wetting forces over time provides an indication of both the wetting ability of the solder paste and the solderability of the electrical component (Figure 6).

The developed apparatus consists of: Figure 1 -Synchronous method test equipment assemblage Figure 2 -The Mini-Crucible Figure 3 -The Test Jig Holder Figure 4 -The Test Jig Plate Figure 5 -The typical force measurement curve Figure 6 -The "Synchronous" test measurement curve Figure 7 -Example of applying solder paste to a test jig plate Figure 8 -Required electrical component orientation to conduct a test The measuring system to which this assembly is mounted must satisfy the following requirements a) The range of measurement of the wetting force must be -10 mN to +10 mN.

b) The deviation sensitivity of the force sensor needs to be better than 0,5 mN/pm.

C) The resolution of the force sensor should be better than 0,01 mN.

d) A recorder should be used to record the output data to a computer.

e) The time resolution of the record should be better than 0,1 s.

f) The electrical and mechanical noise of the system must not exceed 10 % of the signal.

The lift system must be able to provide an immersion depth of the specimen into the solder paste on the test jig plate to an accuracy ±0,05 mm, so that the maximum depth is equal to the depth of the test jig plate. The position resolution must be controllable to better than 0,02 mm. The speed must be 0,5 mm/s to 5 mm/s.

The heating system must be capable of controlling the set temperature in the heated bath and mini-crucible. (Figure 2 Example of the temperature profile) To carry out a test, first apply the selected solder paste to the test jig keeping the surface flat. Figure 7 shows an example.

Fit an electrical component to the measuring system in the usual manner, ensuring that it is in the correct orientation to conduct either a normal or this synchoronous test method. See Figure 8 Mount the Test Jig Holder onto the adjustable sprung supporting bars Mount the filled Test Jig Plate into the Test Jig Plate Holder and adjust the height so that the component is sitting just above the surface of the solder paste close to the electrical component termination that is to be measured.

The test procedure will now be automatically by the control module.

Withdraw the specimen from the molten solder paste when measurement is finished. Recording of the result is completed when the force reaches to a stable state or specified duration.

Presentation of the result The recorder records the force acted to the specimen in the vertical direction.

The force acted to the upper direction (pushing force or buoyancy) is recorded as a negative value, and the force acted downward to the specimen (wetting force) is recorded as a positive value.

A typical shape of the test curve obtained is shown in Figure 6.

DRAWINGS

1 Specimen 8 Mini crubicle 2 Test jig plate 9 Support bars with spring 3 Solder paste 10 Sensor 4 Heating bath 11 Transducer Lift 12 Recorder 6 Base 13 Controller 7 Test jig plate holder Figure 1 -Key Synchronous method test equipment assemblage * .

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0.5... * S S. * * *. * S.

5,0... * 0 5S S * I S a *s * IS.

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DRAWINGS

Shape Circular indented pan constructed of oxygen-free phosphate copper Dimensions (L,W) Less than 30 mm one side, or less than total area of 900 mm2 Thickness (t) 0,3 mm ± 0,03mm Drawn diameter 9 mm to 10 mm at the bottom, (D1, D2) 13mm to 14mm at the top Drawn depth (h) 0,4 mm ± 0,04 mm Figure 4-Key The Test Jig Plate * S *S.S * S *5 S * ** * .* * S... * S S. S * S S * .5

S SS,

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DRAWINGS key

T0: The time to start measurement. The specimen is brought in contact with solder paste that is melting.

T1: The time at which the output cross the zero line. The downward force of surface tension is exactly equal to the buoyancy force. (Point A in Figure 7).

T2: The time to wetting force reaches to 2/3 of the maximum wetting force (Point B in Figure 6).

T3: The time to withdraw the specimen and the measurement is finish. (Point D in Figure 6).

t1: The time to start wetting.

t2: The time From Point A to B. Fmax The maximum wetting force. (Point C in Figure 6) 2/3 Fmax 2/3 of the maximum wetting force (Point B in Figure 6) Fend: the final wetting force when the measurement is finish Figure 6 -Key Typical output shape of signal in the synchronous method 1U* * I **I.

* I. .I* * * ** I * SI * *0

I * I SI * * S * * **

S * I.

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DRAWINGS Key

1 Test jig plate 2 Solder paste 3 Squeegee 4 Direction of squeegee travel Figure 7 -Key Example of applying solder paste to a test jig plate. S... * * **SS

S..... * * *. S * SS * II

S..... * S S. S * .. * S.

Claims

CLAIMS1 A Synchronous method and Apparatus for testing the Solderability of electrical components using Solder Paste and simultaneously assessing the usability of a Solder Paste 2 An assemblage according to claim 1 that permits the test to be performed whilst minimising the adverse effects of the volatilisation of the flux contained within the solder paste that otherwise compromise the accuracy of the force measurement 3 The assemblage described in Claim 2 comprising the Mini-Crucible, Test Jig Holder and Adjustable Sprung Supporting Arms 4 The ability to accurately isolate and minimise the boiling effects of the solder paste to ensure a meaningful test curve and result