The chronology of PT/35(b): 05/03/1992

5 March 1992

(Worroll / Johnson – see also 11 April 1990 and 23 May 1990 above)

According to their police statements, on this date both officers travelled to Ferranti
International, Oldham, where they interviewed Allan Worroll and caused him to
microscopically examine DP/498, the resin encased sample from DP/347(a), and
asked him to provide a technical description of this item, which he did and is
incorporated into his statement. Worroll also provided a phase diagram, DP/507
(prod 353) to illustrate the differences in structures of tin/lead alloys subjected to heat.

DP507-1

According to the police report Worroll provided a technical description along the lines
of that which he provided for PT/35(b), and he explained that the anomalies apparent
between the two descriptions could be because PT/35(b) was visibly altered by its
close proximity to an explosion. The phase diagram he provided showed the sharp
melting point of electronic grade solder.

Worroll’s manuscript statement (prod 363) records that he examined DP/347(a) and
DP/498 and also DP/501, DP/502 and DP/503, which were enlargements of
photographs of the original fragment (photos 336, 334 and 333 of the RARDE report
respectively) and he gave a further technical description. It appears that this
description corresponds to the 7 points in the description of PT/35(b) listed in DP/141,
which is not a production but which the Commission obtained from D&G. In his
description of DP/347(a) Worroll said:

(1) DP/347(a) is single-sided, there being no evidence of through-hole plate connections [just as he described PT/35(b) DP/141];

(2) the sample is 1 ounce copper clad FR4 laminate – a layer of glass cloth [this
appears consistent with what he said about PT/35(b) in DP/141, although there is more detail in the PT/35(b) description];

(3) the sample has solder mask applied to the non component side and it appears to have been screen printed on. It is approximately 0.0007 inches thick. Worroll could not understand why the “back-side” of the PCB had solder mask [presumably this is for aesthetic reasons, as described by Linsdell in his statement prod 3611 [in his description of PT/35(b) in DP/141 Worroll said solder mask had been applied to both sides of the board, it being a wet epoxy based type either screen printed or brushed onto the board. He could see no reason for the backside of the board to be solder masked. In his 1992 statement Worroll suggested that the reason for the differences in his description of PT/35(b) and DP/347(a) could be that PT/35(b) had been visibly altered by its close proximity to an explosion – although this is not likely to explain why PT/35(b) had solder mask on both sides – this appears to be the only difference between the descriptions of the two samples
here; and Worroll said in his CP that the fragment had mask on one side only];

(4) the tracks are nominally 0.010 inches wide with spacings nominally 0.018 inches between the tracks [this is consistent with his description of PT/35(b) in DP/141];

(5) Worroll said the solderable deposit on DP/347(a) was much thicker than on PT/35(b) [this does not directly correspond to any description of thickness of solder deposit of
PT/35(b), although at point 5 of DP/141 it is recorded that Worroll said the tracks
were coated with pure tin, probably from an electroless tin solution, presumably to aid
solderability];

(6) Worroll said he could not comment on this as no assembly on this
sample had been effected [in DP/141 he stated that normal electronic grade solder had
been used to make the solder connection – presumably because nothing had been
soldered to the connection on DP/347(a) there was no solder present, hence the reason
he could not comment];

(7) he stated that DP/347(a) was a commercially manufactured board [in DP/141 he was recorded as saying the copper pad and tracks suggested PT/35(b) could be home-made, but the machined radius of the board suggested commercial machining operation].

Worroll’s manuscript statement then refers to illustrating the differences in structures
of tin/lead alloys when viewed by scanning electron microscope by him drawing
DP/507, the phase diagram of the tin/lead alloy system. The statement explains that
electronic grade solder has fine grain structure whereas compositions lying well
outside the range e.g. plumbers solder do not have the sharp melting point of
electronic grade solder but melt or cool over a range of temperature and deposit areas
of tin or lead rich alloy dependent on the original composition.

In his CP Worroll was shown DP/347(a) and stated that he did not particularly recall
it, although he could see it was a single sided board that bore many similarities to the
fragment PT/35(b). He said it was not possible to comment on the solder mask on the
board. He noted that the manufacturer used surface mount technology which would
have been fairly high-tech in 1985. He would not have expected the board to have
been manufactured domestically as the quality of the tracking was fairly high. He
thought domestic manufacture would be unable to produce anything that complex due
to the degree of tracking and the close proximity of components. He noted that he
signed the label for DP/347(a) but could not recall carrying out any tests on it. He had
no reason to doubt the police officers if they indicated that he did carry out tests on it.
He was shown DP/498 and likewise had no recollection of examining the sample.

In his DP Worroll did not mention the visit in 1992.

In evidence Worroll was able to recall being visited by police on an occasion when
they brought with them an entire circuit board. There was some questioning from the
advocate depute about exactly what the police asked him to do and there was some
confusion on the part of the witness as to what he was being asked, but he maintained
that he had only been asked to examine the circuit board visually and had not
conducted any tests on it. He was not examined further about the results of his visual
identification or the comparison to PT/35(b).

Comparison between control sample and fragment: Generally Worroll seemed content
that the particular aspects of the control sample were the same as the fragment. He
was recorded as stating that the control sample was only solder masked on the
backside, whereas the fragment was solder masked on both sides, but his position on
both these matters appears to have altered over time (he said at precognition that the
fragment was solder masked on one side only and said he could not comment on the
solder mask on the control sample) and his opinion on whether there was solder mask
on both sides of the fragment was disputed by other experts (above). Worroll also
said the solderable deposits were thicker on the control sample than on the fragment.
This would be consistent with what Wilkinson observed, so the explanations
Wilkinson offered for this, about possible loss of tin and lead because of heating, may
apply. This might be what prompted Worroll’s explanations of the melting point of
electronic solder, as evidenced by his phase diagram (DP/507).

The HOLMES statements of the officers record that, later the same day, the two
officers attended Dr David Johnson’s laboratory at the Centre for Surface and
Material Analysis in Manchester. Dr Johnson examined DP/504 (label 406, the
fragment removed by those at Morton International, see 2 March 92, above) using
Secondary Ion Mass Spectrometry. A brief statement was obtained from Dr Johnson,
who promised to provide a full analysis report including comparisons between the
analyses of DP/504 and PT/35(b) later.

The police report states that following brief comparison between the data held on
PT/35(b) and that which Dr Johnson obtained from DP/347(a) there was nothing to
suggest that the two samples were not the same, and reference is made to his analysis
report which by the time of the police report had been received (DP/510).

Johnson’s manuscript statement (prod 365) basically reflects what is said above. He
also explained that the brief comparison indicated nothing to suggest the two samples
were not the same, confirmation that the two samples were the same was not possible
because of the qualitative techniques used in the testing. Johnson also stated that on
the track side of the new sample the results showed several differences in quality of
metals, particularly lead, present. However, the physical characteristics of the sample
were quite different in terms of the surface conductivity and the fact that the first
sample had suffered heat damage more to the track side that the reverse. Intense heat
could have altered the surface of the track face of the sample.

In his CP Johnson could not recall the visit by police officers in 1992. He was shown
his analysis report, DP/510, and recognised it as his work. He stated that the report
detailed that he was approached again in March 92 by the same police officers [in fact
it was different officers] who asked him to examine another sample. This report
includes the spectra data produced from his previous report on PT/35(b). Johnson
was shown DP/347(a) at precognition but had no recollection of examining the board.
He saw his name on the label and presumed it was the board he used as a control
sample for his second report. He said his report suggested he carried out analytical
procedures on a fragment of the sample board which had been removed previously.
He was shown DP/504 and said this was definitely not mounted by him. He said he
had signed the label and this was the fragment he had used in the additional test. He
washed DP/504 in Heptane, as he had done for PT/35(b). He stressed that his results
were qualitative and were restricted to comparing peaks produced in the spectra. He
stated that the intensities of the peaks were different, which meant the same elements
were present on the surface of the fragments but in different quantities. In summary,
he said PT/35(b) and DP/347(a) were more similar than the other control samples he
used in his first report on PT/35(b) (Sefolam and Dytron). At its highest, he was
prepared to say that there were no substances present which suggested that the two
were not the same, when one looks at the qualities of the substances rather than the
quantities. He stated that he did not bother to compare the composition of the solder
on the tracking side of DP/347(a) and PT/35(b) because the potential for heat damage
could affect the composition of the solder.

In his DP Johnson said that the police asked him to conduct an analysis of the solder
content from the upper side of the board which he agreed to do, but he recalled
explaining to the police that he would consider this invalid as a comparison with
PT/35(b), as PT/35(b) had been shown to be damaged and significantly altered in
constitution. He said he stated this in his report. He stated that he conducted analysis
of the underside of DP/347(a) in the same manner as had been done for PT/35(b) and
showed that the surface chemistry of the two samples were similar, but that this did
not mean that the samples were identical or that they had come from the same
manufacturer.

Johnson did not give evidence. His report, DP/510, was production 355.

Comparison between control sample and fragment: Dr Johnson did not find anything
to indicate that they were not the same, and he was clear in what he said that the heat
exposure suffered by PT/35(b) would alter the constitution of the solder etc., so that,
although there was a difference between the upper side of the two samples, in that the
lead content of DP/347(a) was much more intense than on PT/35(b), this could be
explained by the evident heat damage suffered in particular to that side of the
fragment.

NB Worroll and Johnson’s signatures are visible on the label for DP/347(a).

Advertisements
This entry was posted in Chronology, DP/347(a), Dr Johnson, PT/35(b), Worroll. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s